Oil boiler problem

gorwanvfr

I have been told that my boiler is short cycling? How can I stop it doing it??
this is what happening the boiler is constantly switching on and off on its thermostat which is set to 55oC. It appears that the boiler jacket temp is reaching 55oC turns off the burner the circulating pump continues to run and with in 3 to 4 minutes the water temp drops to 52oC / 53oC and the burner turns back on with in a minute or two the water temp is back up to 55oC and again the burner turns off. The burner continues like this for as long as the heat is turned on

JamesM

If you have a room stat and cylinder stat turned down, and the burner is still coming on every 3 or 4 minutes, then maybe you have a problem, but if the stats are up and you have a few rads on, then I would think that 3 or 4 minutes is OK. If the boiler stays off for too long, then the rads will just cool down.
Jim.

gorwanvfr

Hi James a few more details, started the boiler this morning and took a few readings. the water temp was 10'C at the start it took 35 minutes to get the water up to 60'C at which point the thermostat on the boiler cut only the boiler out. (There are no stats in the house or on the cylinder) the boiler remained off for 20 seconds and then fired again, ran for 3 minutes and then off, Started again after 40 seconds ran for 2 and a half minutes then off for 40 seconds ran again for 2 and a half minutes. the 40 seconds off 2 and a half minutes on this cycle continued until I switched off the heating. The total load on the boiler is 30 rads a 300L tank and 40Sqm of underfloor heating.
The underfloor heating only has a mixing valve that looks like a TRV. the temperature on the supply and return lines on the underfloor heat read 60'C and 40'C the floor itself is running at 22'C.
The original heating system was installed in the house when we purchased it. since them the underloor heating was installed and the new boiler fitted. Don't mind speeding some money on making the system work correctly or better but don't want to throw money away either.
I worked out the heat loading from the rads and the underfloor heating using info from the net and it worked out at 38Kw.
Believe the boiler is 44Kw.
The boiler maintained a 20'C differenial between supply and return while it was running. the system pressure was 1Bar when the system started and went to 2 Bar once the system was up to temperature.
Hope I'm giving you enough info.
I just think it can't be efficient, the boiler cycling like this instead of running and stopping for a longer periods.

JamesM

I am afraid that I am going to be a disappointement to you
As I have said befor, burners are my thing, but I know a bit about the overall system from experience. You seem to know a lot about your own system.

The way I see it is, you have a very efficient boiler with good heat transfer that heats the water fairly quickly. Because the return is 20c cooler than the flow, the water in the boiler cools very quickly, and the thermostat switches the boiler on again to try to keep a constant temperature flowing to the rads etc. If the boiler stopped for a long period, I presume that the temperature in the rads, and the rooms, would fluctuate a lot and it would be uncomfortable.

In older systems, the idea was to circulate the water as quickly as possible and to keep the return temperature as close as possible to the flow - that would keep the burner off longer.

I only jumped in here because none of the experts were answering you - maybe someone will drop by and explain it all clearly

Outkast_IRE

Can i ask a few quick questions
has this been the case since the system was put in?
And it was just pointed out to you recently ?
It does sound like your system is transferring the heat from the water to the building very quickly , this is likely to happen especially with a mix of underfloor and radiators.
Are the underfloor and radiators zoned seperately at all ?
Are there thermostatic rad valves on the radiators ?

gorwanvfr

Outkast_IRE wrote: »

Can i ask a few quick questions
has this been the case since the system was put in?
And it was just pointed out to you recently ?
It does sound like your system is transferring the heat from the water to the building very quickly , this is likely to happen especially with a mix of underfloor and radiators.
Are the underfloor and radiators zoned seperately at all ?
Are there thermostatic rad valves on the radiators ?

We purchased the house 6 years ago and it had a standard boiler driving 30 rads. The house is just over 3500 Sq feet, which is a good bit bigger, then either of the houses my wife and I grew up in (1400). The first year we went through 5000 liters of oil heating the house which seamed excessive. We checked with our parents with regards to oil usage and they where only using around a 1000L.
When I looked at the system the circulating pump seamed very small for the size of the system/ house, so the local plumbing supplies worked out that I needed a bigger pump. I fitted this and straight away the house heated quicker and the amount of oil used dropped dramatically to just under 2000 L. But one thing I noticed both before and after changing the pump was the boiler cut in and out a lot. But to be honest I never thought much about it.
18months ago we extended the house and installed under floor heating in the new kitchen the floor area is approx 400 Sq feet.
Shortly after I decided to change out the old standard boiler for a new modern condensing boiler. Now I know people will say a condensing boiler will only work properly with a complete new system of rads etc. But I disagree even now with the boiler short cycling I can still see water dripping from the condensate drain and water vapor in the exhaust plume and to me that’s money saved.
I just feel that if the boiler ran for longer and stayed off longer it would be even more efficient.
Also my gut feeling is the system needs more thermostats rather then just relying on the thermostat fitted to the boiler.
To answer your questions OutKast
Has this been the case since the system was put in? Yes
and it was just pointed out to you recently? No
It does sound like your system is transferring the heat from the water to the building very quickly, this is likely to happen especially with a mix of under floor and radiators.
Are the under floor and radiators zoned separately at all? The upstairs and downstairs are split with motorized valves. The under floor has a thermostatic valve fitted and its own circulating pump.
Are there thermostatic rad valves on the radiators?
Only one rad has a TCV.

Thanks in advance for any help

Outkast_IRE

Ok if you just put on to heat the radiators is it short cycling after they are up to temp, after a hour or two is it still short cycling if its just heating radiators.
If you just heat underfloor only is it short cycling after a hour or two ?
Is the boiler burner in a self contained unit like the glavanised boxes for outdoors. If yes is there any chance that flue gas is escaping into the box this can cause a short cycle issue.

The reason i thought thermostatics might help is that when the rooms start reaching temp the valves will close and temporarily cut down the boilers work load.

gorwanvfr

If the house is cold and the heat is turned on the boiler will run constantly for 35 to 40 minutes (Rads, under floor and water tank all in the system). At this point the flow water coming from the boiler will be 60°C, which is the setting of the thermostat on the boiler, so the boiler turns off. Then it starts its short cycling 40 seconds off 2 and a half minutes on. May be the differential on the boiler thermostat is not big enough???
My thinking is using the boiler thermostat to control the system is a poor design. I don’t mind spending some money and getting it right but don’t want to be throwing money away.
At the moment there are no TRV’s fitted (apart from the one on the under floor system) and there are no thermostats in the house.
So the only control in the system is the one fitted on the boiler. I’m strongly thing about fitting TRV’s and an automatic bypass valve (pressure) to protect the system from dead heading.
Forgot to add the boiler in a boiler house and draws it's air through a snorkel

Outkast_IRE

Can you turn on your boiler just to heat radiators or only to heat underfloor not both and see what way it responds when its heater one or the other not both.

gorwanvfr

Outkast_IRE wrote: »

Can you turn on your boiler just to heat radiators or only to heat underfloor not both and see what way it responds when its heater one or the other not both.

Can't turn off the under floor heating (have attach pics of the control set up that the plumber installed) Looks a bit crude?
With the rads turned off the boiler just heats the water quicker and then goes on it short cycling thing

Outkast_IRE

nice of him to use permanent maker on your wall . If i was you at this stage get a reputable oil burner service man and see what he makes of it . He will prob know since he is working on them all the time.
If it goes into short cycling when its heating water only then that is key piece of information to me the points to problem at the boiler/burner end of things .
I wonder if the baffles in the boiler are corroded/damaged or really dirty.
At this stage im just guessing id have to be there to see it to help ya any more.

wing52

You should check the hot water pipes into the cylinder

There may be a restrictor/balancing valve open too much.

On most systems,they're only open 1.5 -2 turns to stop

the boiler short cycling.That appies to all boilers,notjust the newer

ones. Hope that helps.

JamesM

Outkast_IRE wrote: »

nice of him to use permanent maker on your wall . If i was you at this stage get a reputable oil burner service man and see what he makes of it . He will prob know since he is working on them all the time.
If it goes into short cycling when its heating water only then that is key piece of information to me the points to problem at the boiler/burner end of things .
I wonder if the baffles in the boiler are corroded/damaged or really dirty.
At this stage im just guessing id have to be there to see it to help ya any more.

I don't think that an ordinary service guy would have great knowledge of the design and layout of a system like that, with its mix of rads and underfloor heating. When you turn off the rads, the boiler is still heating the underfloor piping - that's still a lot of water travelling around the pipes that has to be heated.
Is there any chance that the pump is working backwards and sending cold water into the top of the boiler and cooling the thermostat very quickly - bringing on the burner sooner than normal. I presume that if you got a new condensing boiler that you also got a new burner with it and that it is matched to the boiler, correct nozzle size etc.
As Outkast said, it's difficult to know without seeing the system.
Jim.

gorwanvfr

JamesM wrote: »

I don't think that an ordinary service guy would have great knowledge of the design and layout of a system like that, with its mix of rads and underfloor heating. When you turn off the rads, the boiler is still heating the underfloor piping - that's still a lot of water travelling around the pipes that has to be heated.
Is there any chance that the pump is working backwards and sending cold water into the top of the boiler and cooling the thermostat very quickly - bringing on the burner sooner than normal. I presume that if you got a new condensing boiler that you also got a new burner with it and that it is matched to the boiler, correct nozzle size etc.
As Outkast said, it's difficult to know without seeing the system.
Jim.

Hi Jim I have to agree with you about getting and ordinary service guy to look at the system. The boiler, burner and flue where all replaced together, it all came new from Firebird so guessing it is correct. Both pumps are installed correctly with regards to flow that was one of the first things I checked. The gate valve on the hot water tank is only open one turn to give a 10°C differential on the coil inlet and outlet.
I'm just wondering if the system is working correctly. Here’s my thinking once the complete system is up to temperature (60°C) the thermostat on the boiler cuts the burner out, since my boiler is 60 feet away from the house (boiler is located in garage) there has to be certain amount of heat lost both on the flow and return to and from the boiler.
Since the differential on the boiler thermostat is only2°C which is quite small this might be what’s causing the short cycling just due to heat loss in the flow and return pipes to my house??
I have an electronic thermostat, which allows the user to set the differential anywhere from 1°C to 25° and the cutout point from 40°C to 80°C. This way I could increase the cut out point to say 70°C and the differential to 10°C. By doing this it might even out the on off cycles. And keep the temp in the house pretty much the same.

JamesM

The boiler thermostat is electronic, and you can set the differential ? These new fangled gadgets I haven't seen one before.
Maybe 10°C is too much, start with 5°C and see how it goes. That should certainly stretch out the off time.
Jim.

Outkast_IRE

just read over your info again a 38kw load on a 45kw boiler
and it could be more as your just working it out rough.
IF it was me i would have a bigger boiler , i dont know exactly whats the problem is without seeing it but for me a bigger boiler would increase the time needed between cycles.

gorwanvfr

Outkast_IRE wrote: »

just read over your info again a 38kw load on a 45kw boiler
and it could be more as your just working it out rough.
IF it was me i would have a bigger boiler , i dont know exactly whats the problem is without seeing it but for me a bigger boiler would increase the time needed between cycles.

Having bounced the ideas around on the forums I think the problem is the differential on the standard thermostat. The fact it’s only 2°C. A bigger boiler would just make the on time even shorter as it could heat the water (circuit) quicker The size of the boiler would have no effect on the cooling of the water.

Outkast_IRE

Oh ya differential is first thing , but we are doing boiler rating vs heating loads in college at the moment and everthing we are being told says bigger boiler means less cycles usually , depending on the system being set up correctly. A larger boiler wouldnt mean more cycles it would mean less as you have more heated water at your desired temp being ready . meaning less cycles .

gorwanvfr

Outkast_IRE wrote: »

Oh ya differential is first thing , but we are doing boiler rating vs heating loads in college at the moment and everthing we are being told says bigger boiler means less cycles usually , depending on the system being set up correctly. A larger boiler wouldnt mean more cycles it would mean less as you have more heated water at your desired temp being ready . meaning less cycles .

Oh how I would love to be in the class, I would inundate the instructor with questions.
I just can’t see how a bigger boiler would solve my problem.
Here’s my thinking (forgive my terminology). The amount of water to heat is controlled by the capacity of the system. When I say the capacity, I mean the water loop coming from the boiler to the rads/ under floor and the coil in hot water cylinder. Now lets say the system is cold and the boiler kicks in, it will stay running until the water in the system (water loop) reaches the cut out point of the thermostat on the boiler (60°C). If there is no heat being transferred from the system (water loop) to the rads/ under floor or cylinder then the temperature in the loop will remain at 60°C and the boiler will stay off, if heat is transferred and the temperature falls below 58°C then the boiler kicks in and the cycle starts again.
If the boiler (44Kw) for example can raise the loop temperature by 1°C a minute then after 2 minutes the loop temperature is back up to 60°C and the boiler cuts out. The off time will totally depend on the heat load and the time taken to drop the heat in the system loop by 2°C.
Now if the boiler is bigger (88Kw) and it can raise the loop temperature by 2°C a minute, after 1 minute the loop temperature is back up to 60°C and the boiler cuts out.

I could see if the boiler was under sized the following problems might occur

• It might never be able to reach the 60°C (due to heat load) and run for as long as the main switch is on.
• The house might take forever to heat up.
• The on cycle might run for a lot longer (but the off cycle will still be controlled by the heat loss in the system loop)

Please do not take offence to my questions/thinking, I’m just trying to get a better understanding of my system and in the process perhaps improve its efficiency.

Outkast_IRE

As i said in previous post its all dependant on system set up theres such a combination of controls available at the moment that it is causing people headaches as theres not enough people experienced with them .
I see your argument , and just at a quick glance it does seem valid .

your right a bigger boiler wont solve your problem(just reread all posts ) if the differential is that low .
Lets say your system is thouroghly checked all controls and differential set properly , burner checked and set properly. If you were still experiencing a short cycle then a bigger boiler burner is a viable option .

Argueing the pros and cons of systems is one of the high points of college !!

tommy 10

Just a quick reply for you ,you could have a hyper active stat but i would turn off the underfloor heating and about six rads turn on the heating and see what happens if all stays the same adjust the stat , if the cycle time improves you need a bigger boiler-burner

JamesM

gorwanvfr wrote: »

Having bounced the ideas around on the forums I think the problem is the differential on the standard thermostat. The fact it’s only 2°C. A bigger boiler would just make the on time even shorter as it could heat the water (circuit) quicker The size of the boiler would have no effect on the cooling of the water.

You say above that it's a standard stat - but it's not, I have never seen a stat where you can adjust the differential supplied as standard with a Firebird. Have you tried it with the differential set to 5 or 10 degrees as we discussed a few days ago ?
Jim.

tommy 10

I have worked with firebird boilers for about 20 yrs now and never seen the stat you refer to but hey things change all the time , as regard the boiler size bigger boiler means bigger resevoire of hot water , longer time to move , = longer time before stat gets cold and boiler kicks in again

gorwanvfr

tommy 10 wrote: »

I have worked with firebird boilers for about 20 yrs now and never seen the stat you refer to but hey things change all the time , as regard the boiler size bigger boiler means bigger resevoire of hot water , longer time to move , = longer time before stat gets cold and boiler kicks in again

Sorry for the confusion the standard stat that came with the boiler has a 2°C differential. I have my own adjustable stat that allows all parameters to be set.
Tommy 10 have to agree and disagree about a bigger boiler just can’t see the difference it will make in my case with regards to efficiency. Yes the boiler would take longer to cool down and so remain off longer but it would also run a lot longer heating up extra water that it not needed. I really think it is more down to a lack of controls on my system.
James am not currently at home so it will be next week before I can adjust the differential and report back on the findings
Thanks for all the suggestions and help guys

tommy 10

By its very nature thats what cycle time means your heat up time will be longer but your cool down time will also be longer , to do this simply if you have 10 pints of hot water and your pump moves 2 pints per min it will be 5 mins for cold water to reach the stat 8 pints will take 4 mins and so on your boiler ability to make hot water should always out strip its use of it . Going by your figures using all the info you have provided with the correct boiler your cycle times should work out at around 6 mins burn time and 8- 10 mins off . these are rough figures but should give you an idea of what your looking for on a correct cycle time , try turning off some of the system and see what happens , good luck with your reserch .

gorwanvfr

OK here’s the update.
Set the thermostat to 65°C and the differential to 13°C. Made a huge difference the boiler runs now for 2minutes and 40 seconds and stays off for 2minutes15 seconds once the house is up to temp. With the settings on the thermostat as above the house is a very comfortable temperature. Just have to wait and see if it improves the economy of the boiler. If nothing else the boiler should last a bit longer since it’s cycling less.