Gloworm 18hx: Gas boiler under specced?

ravendude

Hi there,
We had our heating system upgraded last year, - converted from oil and zoned etc.
The house is circa 2000sq feet and comprises 15 rads., 5 or 6 would be largish size, approx 1.5 metres long.

Now when we have upstairs zone only running it heats up very fast ( 10 to 15 mins ) and rads are piping hot. With the downstairs zone only running ( downstairs is a bit bigger as there is a sunroom and upstairs is a dormer) it takes a nice bit longer, 20 to 30 mins.

With both zones on, the system is very ineffective. An hour later and the rads downstairs are not properly warm. Upstairs is reasonably ok but still takes a long time.

The gas boiler is a gloworm 18hx, is anyone familiar with this one? Is it too small for this number of rads, or could it be a balancing problem or something?

I'm going to talk to the contractor but would like to have some idea of what the issue is before doing so.

Thanks!

Robbie.G

Your boiler is to small for your house.An 18kw boiler would be used in a average house a house of 2000sq ft would need an 30-35kw boiler

corkgsxr

61k btu could be a touch small alright


Get your rad sizes. Work out the btu's add in your cylinder. And then you have your boiler size.

Presuming your rads are right sized

ravendude

Hmm,

How do I know how many btu/kw each rad requires?
I'm convinced now the boiler is too small for the job. It doesn't even heat the downstairs properly, some rads arent properly warm. When I turn off a few of the rads the ones left on start hopping hot. It's impossible to get any heat out of it if both the upstairs and downstairs zones are on.

Also, this is a condensing boiler, do these only require a less kw output than normal to heat the same number of rads, or is it just that they're more efficient in the gas used? My parents house which is quite a bit smaller than ours (1500 sq feet versus 2000+) has a 25kw (vokera mynute 28se) non condensing boiler. 18kw sounds way too low for ours.

Also, our gas bills are huge, I'm thinking this is because the boiler is firing all the time, similar to trying to boil water in a saucepan but only being able to simmer all day. Would the very high gas bills be explainable by the underpowered boiler?

Would all I describe above be typical symptoms of having too small a boiler?

Thanks sincerely for any help, this is really stressing us out, but a least now we might be able to make a strong argument and have some chance of getting the contractor to rectify

Robbie.G

As a previously said the boiler is seriously undersized.Yes you are right regarding the gas bills the boilers always on
Have a go on this and work if out for yourself keep the results and talk to your installer.
http://www.idhee.org.uk/calculator.html

Dtp79

ravendude wrote: »

Hmm,

How do I know how many btu/kw each rad requires?
I'm convinced now the boiler is too small for the job. It doesn't even heat the downstairs properly, some rads arent properly warm. When I turn off a few of the rads the ones left on start hopping hot. It's impossible to get any heat out of it if both the upstairs and downstairs zones are on.

Also, this is a condensing boiler, do these only require a less kw output than normal to heat the same number of rads, or is it just that they're more efficient in the gas used? My parents house which is quite a bit smaller than ours (1500 sq feet versus 2000+) has a 25kw (vokera mynute 28se) non condensing boiler. 18kw sounds way too low for ours.

Also, our gas bills are huge, I'm thinking this is because the boiler is firing all the time, similar to trying to boil water in a saucepan but only being able to simmer all day. Would the very high gas bills be explainable by the underpowered boiler?

Would all I describe above be typical symptoms of having too small a boiler?

Thanks sincerely for any help, this is really stressing us out, but a least now we might be able to make a strong argument and have some chance of getting the contractor to rectify

Or write down all your rad sizes here and somebody will calculate for you. Include your cyclinder size

ravendude

That would be great. I'll collate the measurements and put them up this evening.

One other question, - I have a feeling that he might say that because its zoned the "norm" is just to have the boiler sized for one of the zones at a time, ie. and not for having the heating going on the 2 zones. (Even though I believe this is inadequate even just for the ground floor).

This sounds insane to me, - but is it something that installers would commonly do?

spireland32

As well as your boiler undersized your pump could well be too small. From what youve said youd want a 6m head pump.

Dtp79

ravendude wrote: »

That would be great. I'll collate the measurements and put them up this evening.

One other question, - I have a feeling that he might say that because its zoned the "norm" is just to have the boiler sized for one of the zones at a time, ie. and not for having the heating going on the 2 zones. (Even though I believe this is inadequate even just for the ground floor).

This sounds insane to me, - but is it something that installers would commonly do?

Insane is right

shane0007

I have been following this thread with some interest & everybody has hit the nail on the head. The boiler is very much under-sized for a 2,000sqft house. All boilers, especially gas boilers should be sized correctly for the extreme demand, i.e. all zones on at the same time & not for just on the off chance only one zone is demanded!
The reason for gas boilers being more important over an oil boiler, is because they can modulate down to suit the demand when only one zone is demanding. An oil boiler is better being SLIGHTLY under-sized so reduce short cycling & keep the boiler in its most efficient state, i.e. condensing.

ravendude

Some progress today, spoke at length this morning to the installer. He accepted responsibility and got on it straight away in fairness, no real excuse though, - I didn't want to force the issue at this stage as I am more interested in getting the issue resolved. He got on the case straight away So I need to commend him for that much at least, otherwise it could have been a real headache.

He came out latish this evening with a glow worm service engineer.
Im not sure of the precise details, Apparently the glow worm hx is ranged so the service engineer did some mod and tuning to convert it into a 30kw boiler. Anyone know if this makes sense or is possible? I checked the tech specs and they are the same in every way (case size, weight etc.) bar output, s o it seems feasible. Am told theres no effect on warranty as work took place by glow worm service guy.

Very early trial of the system with all zones running suggest a dramatic improvement with rads hopping. I'm not clear yet how long it takes the system to crank up as I got home late, but will watch it closely overly the coming week and give it a good testing at the weekend.

Thanks everyone for all the info so far it really made a difference in making my point irrefutable and progressing this issue. Not out of the woods yet, but it's looking better at least

spireland32

ravendude wrote: »

Some progress today, spoke at length this morning to the installer. He accepted responsibility and got on it straight away in fairness, no real excuse though, - I didn't want to force the issue at this stage as I am more interested in getting the issue resolved. He got on the case straight away So I need to commend him for that much at least, otherwise it could have been a real headache.

He came out latish this evening with a glow worm service engineer.
Im not sure of the precise details, Apparently the glow worm hx is ranged so the service engineer did some mod and tuning to convert it into a 30kw boiler. Anyone know if this makes sense or is possible? I checked the tech specs and they are the same in every way (case size, weight etc.) bar output, s o it seems feasible. Am told theres no effect on warranty as work took place by glow worm service guy.

Very early trial of the system with all zones running suggest a dramatic improvement with rads hopping. I'm not clear yet how long it takes the system to crank up as I got home late, but will watch it closely overly the coming week and give it a good testing at the weekend.

Thanks everyone for all the info so far it really made a difference in making my point irrefutable and progressing this issue. Not out of the woods yet, but it's looking better at least

Yes this is possible, however you need to make sure you have an adequate gas supply as you have now nearly doubled your boiler size. Your installer got away with that one

ravendude

Would it be common to have a lower gas supply for some reason? Would it be a valve or something into the house that would be the issue?

We just got connected up to gas last year (it was oil previously), so I would hope there is an adequate supply.

He is coming again at the end of the week to see if everything is ok and check balancing etc. so i will ask him to check all this stuff then.
I already asked him about the pump, and he said he would verify it, but I need to get confirmation (forgot about this one with everything going on).

House was lovely and warm this morning though, - so indications are good

Dtp79

ravendude wrote: »

Would it be common to have a lower gas supply for some reason? Would it be a valve or something into the house that would be the issue?

We just got connected up to gas last year (it was oil previously), so I would hope there is an adequate supply.

He is coming again at the end of the week to see if everything is ok and check balancing etc. so i will ask him to check all this stuff then.
I already asked him about the pump, and he said he would verify it, but I need to get confirmation (forgot about this one with everything going on).

House was lovely and warm this morning though, - so indications are good

An adaquare gas supply generally means the size of the gas pipe going to your boiler. It should be at least 3/4 inch for A rated boilers

ravendude

Dtp79 wrote: »

An adaquare gas supply generally means the size of the gas pipe going to your boiler. It should be at least 3/4 inch for A rated boilers

Thanks for that. I'm 99% sure it is. I'll double check this evening when I get home. The boiler has always been A rated, condensing etc even when at the lower, insufficient KW. so I would expect so.

spireland32

You need enough gas when the boiler is in high fire.To be honest id like to see some inch on your gas supply with a 30kw. New condensing boilers suck/pull the gas through the fan so need an adequate gas supply.

ravendude

What are the implications of too low a supply?
eg. Poorer performance, shorter boiler lifespan? less efficiency?

corkgsxr

emissions go all out of wack too dont they?

ravendude

corkgsxr wrote: »

emissions go all out of wack too dont they?

?
now you have me worried!

Dtp79

ravendude wrote: »

?
now you have me worried!

Carbon monoxide would worry me too!! One other question.... Is your boiler installer a registered gas installer ( RGI )??

ravendude

Dtp79 wrote: »

Carbon monoxide would worry me too!! One other question.... Is your boiler installer a registered gas installer ( RGI )??

Hmm the pipe in looks likw 1 cm wide.
Yes he is a registered installer of course, and I had thought a very reputable one

Dtp79

ravendude wrote: »

Hmm the pipe in looks likw 1 cm wide.
Yes he is a registered installer of course, and I had thought a very reputable one

Take a pic of the of the boiler where the pipes are going into it

shane0007

ravendude wrote: »

He came out latish this evening with a glow worm service engineer.
Im not sure of the precise details, Apparently the glow worm hx is ranged so the service engineer did some mod and tuning to convert it into a 30kw boiler. Anyone know if this makes sense or is possible? I checked the tech specs and they are the same in every way (case size, weight etc.) bar output, s o it seems feasible. Am told theres no effect on warranty as work took place by glow worm service guy.

I would love to know what he did to convert an 18kw boiler into a 30kw!
Was the heat exchanger & burner swapped out? 30kw boiler would generally have larger pipework than an 18kw also.
Boiler data plate/serial number would also need to be changed for future RGI's working in the boiler.

Odd if you ask me!

spireland32

shane0007 wrote: »

I would love to know what he did to convert an 18kw boiler into a 30kw!
Was the heat exchanger & burner swapped out? 30kw boiler would generally have larger pipework than an 18kw also.
Boiler data plate/serial number would also need to be changed for future RGI's working in the boiler.

Odd if you ask me!

Its the same boiler 12kw-30kw you can change it to any one in the range, if you know the codes! However it would have to be marked for future reference as you say. OP your installer needs to check what mb he has at the test point with boiler in high fire, to check gas pressure.

ravendude

I measured the copper pipe in with calipers, its a half inch widee see below.

Should I be concerned? is it a safety issue.
Maybe I should verify with the rgi?

wing52

Re programming the boiler is all very well,

but did the tech re-rate the gas valve as as well?

spireland32

Its how far the the run from the meter is... and how far he ran 3/4 and how much 1/2 there is. Its a half inch gas cock on the boiler so he has to go to half inch there. As I said id like see some inch on that gas line with a 30kw

Dtp79

ravendude wrote: »

I measured the copper pipe in with calipers, its a half inch widee see below.

Should I be concerned? is it a safety issue.
Maybe I should verify with the rgi?

Did the glow worm guy not notice the 1/2 pipe?

ravendude

wing52 wrote: »

Re programming the boiler is all very well,

but did the tech re-rate the gas valve as as well?

Not sure how to kniw that.

The service engineer wss actually from glow worm. So surely he would kniw whst he wss dojng.

Is the half inch pipe a big deal? Im referring to the copper pipe going into the unit from below in the photo attached to my last post above.

Ive attached a photo of it below with a calipers

corkgsxr

Looking at the parts list the 18 and 30 looks to have different part numbers

spireland32

Its the exact same boiler trust me I know these boilers inside out and upside down. Have only being fitting these since 2007. Have fitted a huge number of these... the things you can do IF you know the codes..

You need to check your gas pressure at the gas cock with boiler in high fire. This will tell you alot about your gas line. It should be gas rated and FGA'd

wing52

L 2 ect.....::cool:

Dtp79

spireland32 wrote: »

Its the exact same boiler trust me I know these boilers inside out and upside down. Have only being fitting these since 2007. Have fitted a huge number of these... the things you can do IF you know the codes..

Where do you get the codes from?

shane0007

So basically all their range is the same boiler & then just range rated down!
Is a 30kw boiler the same price as an 18kw?
I personally cannot see the point of it. The heat exchanger & burner must be over-sized across the range apart from top end.
Working pressure on high fire will determine pipe sizing. Gas rating will determine boiler is outputting as per MI's (+5 / -10%).

ravendude

shane0007 wrote: »

So basically all their range is the same boiler & then just range rated down!
Is a 30kw boiler the same price as an 18kw?
I personally cannot see the point of it. The heat exchanger & burner must be over-sized across the range apart from top end.
Working pressure on high fire will determine pipe sizing. Gas rating will determine boiler is outputting as per MI's (+5 / -10%).

While I'm pretty clueless when it comes to boilers specifically, - manufacturers do this all the time, you'd be surprised at how common it is generally. Often its cheaper (and more efficient in terms of support and servicing processes) to just limit or stunt a product for the cheaper/lower end market than to produce, source and support different components. Why spend money designing a product differently , then documenting it differently and training servicing staff differently and training phone support staff differently when you can just make it homogeneous and have a setting to make the product different

It happens all the time especially where there is some software or firmware involved.

shane0007

ravendude wrote: »

Why spend money designing a product differently , then documenting it differently and training servicing staff differently and training phone support staff differently when you can just make it homogeneous and have a setting to make the product different

Because it is the right thing to do! No varying training required, just a correctly sized burner & heat exchanger to output the required kw.

ravendude

OK, the saga continues. Any advice is sincerely appreciated (as it has been to date!)

The situation was much improved by the boiler range mod to 30kw. I'm not convinced though that it is outputting the full 30kw.

The pipes into the immediate boiler are definitely half inch pipes. The gas meter is probably 15 metres away from the boiler. From what I can tell, there is 3/4 inch pipe from the meter to the wall of the house, on the other side of where the boiler is. There is casing around the gas pipes where they enter the wall (where the footpath meets the wall) of the house up into the boiler. It turns from 3/4 inch to 1/2 inch at that point from what I cal tell. ie.

I asked whether a meter rating was done and the indication was "yes" but the answer was a bit fuzzy, - saying the glow worm technician would have done all of that.

When the full system is going, (downstairs zone, upstairs zone and water) it takes close to 50 minutes for all the rads downstairs to get fully hot, ie. piping hot and uncomfortable to the touch, where they are properly emitting heat. They do all get to that point though in fairness, its just that it seems a bit slow to me. After half an hour, most of them would be hot, but not all.

The installer is saying that its the nature of the system that was there prior to the boiler upgrade etc. and the boiler and supply is fine.
Is this reasonable? or is it outside the bounds of acceptability, ie. should I accept this?

Also, a flue test was mentioned, what is the purpose of this?

shane0007

ravendude wrote: »

OK, the saga continues. Any advice is sincerely appreciated (as it has been to date!)

The situation was much improved by the boiler range mod to 30kw. I'm not convinced though that it is outputting the full 30kw.

The pipes into the immediate boiler are definitely half inch pipes. The gas meter is probably 15 metres away from the boiler. From what I can tell, there is 3/4 inch pipe from the meter to the wall of the house, on the other side of there the boiler is. There is casing around the gas pipes where they enter the wall of the house into the boiler. It turns from 3/4 inch to 1/2 inch at that point.

I asked whether a meter rating was done and the indication was "yes" but the answer was a bit fuzzy, - saying the glow worm technician would have done all of that.

When the full system is going, (downstairs zone, upstairs zone and water) it takes close to 50 minutes for all the rads downstairs to get fully hot, ie. piping hot and uncomfortable to the touch, where they are properly emitting heat. They do all get to that point though in fairness, its just that it seems a bit slow to me. After half an hour, most of them would be hot, but not all.

The installer is saying that its the nature of the system that was there prior to the boiler upgrade etc. and the boiler and supply is fine.
Is this reasonable? or is it outside the bounds of acceptability, ie. should I accept this?

Also, a flue test was mentioned, what is the purpose of this?

Ok very easy to confirm. Ask the installer what is the WORKING PRESSURE AT THE GAS INLET when the boiler is in FORCED HIGH FIRE.
Then ask the installer or the Gloworm engineer to confirm the NET GAS RATE of the appliance again when it is in forced high fire.
The WP test will confirm 100% whether or not the pipe supplying gas to the boiler is of adequate size. The GR test will confirm 100% the ACTUAL output of the boiler in high fire.

If these are all up to expectations then the problem is either the boiler is still too small & a full heat loss calculation should be carried out or you have a circulatory/system problem.

ravendude

Thanks for that. Will follow up on that.

Going to do another test now, which is to time how long it takes for the downstairs zone rads to come to temperature. I think this would be a strong indication of whether its still a boiler/supply issue or a circulation issue.

Would 45 to 50 mins be unacceptable do you think for rads to get piping hot with all zones on (downstairs, upstairs and water tank)? The installer is trying to suggest that its at the upper end but still reasonable.

shane0007

ravendude wrote: »

Would 45 to 50 mins be unacceptable do you think for rads to get piping hot with all zones on (downstairs, upstairs and water tank)? The installer is trying to suggest that its at the upper end but still reasonable.

I would agree with him.
Measure each rad, length x height (mm), & state whether single or double. Also volume of your dhw cylinder. I will do a boiler size calculation for you. This will only be a system size calculation for the system that is installed & will not be determine whether the rad is sized correctly for the room or not. I would need room sizes for that along with number of external walls, floor types, etc. for that.

ravendude

shane0007 wrote: »

I would agree with him.
Measure each rad, length x height (mm), & state whether single or double. Also volume of your dhw cylinder. I will do a boiler size calculation for you. This will only be a system size calculation for the system that is installed & will not be determine whether the rad is sized correctly for the room or not. I would need room sizes for that along with number of external walls, floor types, etc. for that.

Sincerely appreciated....
There are 15 rads in all.

Downstairs:
All 20 inches/50.8 cm high
Lengths follow for doubles:
- 128
- 95
- 153
- 107
- 95
Singles downstairs:
- 105
- 95

Heights are mixed upstairs, L for length, h for height
Sunroom:
- 200L X 40H
- 200L x 40H

Upstairs:
- 80L x 50H
- 80L x 50H
- 80L x 60H
- 50L x 50H
- 50L x 50H
- 70 L x 50H

I don't know precisely how big the cylinder is. I know it's pretty basically the biggest that you can get in a normal copper cylinder as I remember he was saying a steel one would need to be fitted at greater cost if we wanted to go bigger, 500L sticks out in my mind for some reason.

shane0007

Are upstairs & sunroom singles or doubles?

I would doubt very much your DHW cylinder is 500 litres. Probably 180L. Measure the height & the diameter. Multiply 3.142 x (1/2 diameter x 1/2 diameter) x height. Don't include the insulation, approx 50mm each side. Eg: height = 1.5m. Diameter = 600mm including insulation => less 100mm = 500mm.
3.142 x (0.250 x 0.250) x 1500 = volume = 294 litres so this example would be a 300 litre cylinder.

ravendude

shane0007 wrote: »

Are upstairs & sunroom singles or doubles?

I would doubt very much your DHW cylinder is 500 litres. Probably 180L. Measure the height & the diameter. Multiply 3.142 x (1/2 diameter x 1/2 diameter) x height. Don't include the insulation, approx 50mm each side. Eg: height = 1.5m. Diameter = 600mm including insulation => less 100mm = 500mm.
3.142 x (0.250 x 0.250) x 1500 = volume = 294 litres so this example would be a 300 litre cylinder.

Sorry I missed this last night. I'll measure it this evening when I get home. I think I might have been mixed up with gallons and litres, perhaps it was 50 or 60 gallons. Def remember it being the biggest copper cylinder available though.

ravendude

So Cylinder details are as follows:
Measurements are approximate (ie. to the best of my ability!).
The boiler has manufacturer built in insulation. They do include the insulation, so I guess the diameter would be 10cm (2 X 50mm) less than indicated below?

Height: 130cm
Width (Diameter): 47cm (probably 37cm without insulation?)
Circumference: 160cm

Thanks!

I might be speaking to the installer later today so I'll ask him to confirm the size.

shane0007

ravendude wrote: »

So Cylinder details are as follows:
Measurements are approximate (ie. to the best of my ability!).
The boiler has manufacturer built in insulation. They do include the insulation, so I guess the diameter would be 10cm (2 X 50mm) less than indicated below?

Height: 130cm
Width (Diameter): 47cm (probably 37cm without insulation?)
Circumference: 160cm

Thanks!

I might be speaking to the installer later today so I'll ask him to confirm the size.

Upstairs & sunroom rads? Singles or doubles?

ravendude

shane0007 wrote: »

Upstairs & sunroom rads? Singles or doubles?

Those are all double, - newer type rads also to downstairs (different bleeding valves) due to sunroom extension and dormer conversion.
Thanks!

shane0007

ravendude wrote: »

So Cylinder details are as follows:
Measurements are approximate (ie. to the best of my ability!).
The boiler has manufacturer built in insulation. They do include the insulation, so I guess the diameter would be 10cm (2 X 50mm) less than indicated below?

Height: 130cm
Width (Diameter): 47cm (probably 37cm without insulation?)
Circumference: 160cm

Thanks!

I might be speaking to the installer later today so I'll ask him to confirm the size.

Nothing major there, about 160 litres. Bigger than average but not the largest.

shane0007

34kw required in total to suit the rads. If they are sized correctly for each room, then it should be fine.
Modulation 30kw (if it really is a 30kw) should be also fine on a modulating gas boiler.

Dtp79

shane0007 wrote: »

Nothing major there, about 160 litres. Bigger than average but not the largest.

Was the appliance gas rated yet?

ravendude

Thanks so much for the above.
Is the glowworm boiler a modulating gas boiler? I believe so. If so I think we might be in the right ballpark. The boiler is on forced high fire also if that matters?

The installer says that the glow worm engineer did rating, flow, pressure tests etc. and would have done so for warranty reasons. So, I either need to take his word for it or get someone independent to confirm. Things are looking better now though. He showed me the pipe that comes into the house wall. It is 3/4 inches and turns into 1/2 inch inside the house with just a couple of feet of 1/2 inch to the boiler. The boiler only accepts a 1/2 inch in - so its probably likely its getting the full supply as most of the piping is 3/4 inch from the gas meter.

A couple of small developments that seem to have made a decent difference. Things seem to be operating quite a bit better now.

The installer balanced the rads yesterday between upstairs and downstairs, - seems to have a good effect and downstairs rads are more responsive now. I need to time it properly over the weekend, - but the house is certainly getting very warm now and rads are all hopping.

Also, I rescheduled the water zone so it doesn't clash with the others (no need to have water on at the same time really). This has helped a lot.

My sincere, genuine thanks to everyone for the advice. It enabled me to ask the right questions and ensure I got this sorted! It has made a real difference to the comfort levels of my family over the last week. Thanks!

Dtp79

ravendude wrote: »

Thanks so much for the above.
Is the glowworm boiler a modulating gas boiler? I believe so. If so I think we might be in the right ballpark. The boiler is on forced high fire also if that matters?

The installer says that the glow worm engineer did rating, flow, pressure tests etc. and would have done so for warranty reasons. So, I either need to take his word for it or get someone independent to confirm. Things are looking better now though. He showed me the pipe that comes into the house wall. It is 3/4 inches and turns into 1/2 inch inside the house with just a couple of feet of 1/2 inch to the boiler. The boiler only accepts a 1/2 inch in - so its probably likely its getting the full supply as most of the piping is 3/4 inch from the gas meter.

A couple of small developments that seem to have made a decent difference. Things seem to be operating quite a bit better now.

The installer balanced the rads yesterday between upstairs and downstairs, - seems to have a good effect and downstairs rads are more responsive now. I need to time it properly over the weekend, - but the house is certainly getting very warm now and rads are all hopping.

Also, I rescheduled the water zone so it doesn't clash with the others (no need to have water on at the same time really). This has helped a lot.

My sincere, genuine thanks to everyone for the advice. It enabled me to ask the right questions and ensure I got this sorted! It has made a real difference to the comfort levels of my family over the last week. Thanks!

Get another RGI to gas rate it and check working pressure at boiler. It won't take long to do it