Gloworm 18hx: Gas boiler under specced?

ravendude · 26-01-2013 11:37PM #1

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 · 27-01-2013 12:15AM

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 · 27-01-2013 12:57AM

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 · 27-01-2013 12:58PM

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 · 27-01-2013 01:20PM

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 · 27-01-2013 03:21PM

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 · 28-01-2013 10:45AM

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 · 28-01-2013 10:53AM

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

Dtp79 · 28-01-2013 10:10PM

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 · 28-01-2013 11:30PM

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 · 29-01-2013 12:17AM

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 · 29-01-2013 12:40AM

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 · 29-01-2013 10:21AM

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 · 29-01-2013 10:39AM

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 · 29-01-2013 11:03AM

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 · 29-01-2013 01:29PM

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 · 29-01-2013 03:18PM

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

corkgsxr · 29-01-2013 06:17PM

emissions go all out of wack too dont they?

ravendude · 29-01-2013 06:25PM

corkgsxr wrote: »

emissions go all out of wack too dont they?

?
now you have me worried!

Dtp79 · 29-01-2013 06:31PM

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 · 29-01-2013 08:16PM

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 · 29-01-2013 08:36PM

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 · 29-01-2013 08:41PM

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 · 29-01-2013 09:07PM

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 · 29-01-2013 09:39PM

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 · 29-01-2013 09:44PM

Re programming the boiler is all very well,

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

spireland32 · 29-01-2013 09:59PM

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 · 29-01-2013 10:00PM

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 · 29-01-2013 10:02PM

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 · 29-01-2013 10:04PM

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

spireland32 · 29-01-2013 10:55PM

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

Gloworm 18hx: Gas boiler under specced?

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