Atag boiler only cycling on for a short time

[Jonny]

Hi,

I had an Atag system (heat only) boiler fitted about 3 years ago. It’s model IR24 LPG.
It’s worked fine for the first year or so, but on the second winter (last winter) it had a strange problem where it would only cycle on for about 1 minute and then would go off for about 5 minutes, before then coming on for another minute. As a result the house never really got very warm (only got to about 19°C), despite the room stat being turned up to maximum.
We called out the installer who made a few visits to try to solve this problem, as well as ringing the atag helpline, but the problem persisted. However the boiler started working normally again around February, so we forgot about it and it’s been working perfectly all of this year, until today. It’s gone into the same pattern of cycling on for 1 min, and off for about 5, so as a result the house isn’t getting very warm.
This is getting very frustrating, so has anyone got any ideas about why this could be happening, bearing in mind it only seems to happen in colder weather. Please ask for any more information if required, I have no idea what could be relevant.
Thank you

 

[gmartine]

It sounds to me like your anti-cycle feature is kicking in so the flow temp setting is perhaps too low especially when the weather gets colder. Do you know how to access and use the controls for the boiler?

 

[Jonny]

It sounds to me like your anti-cycle feature is kicking in so the flow temp setting is perhaps too low especially when the weather gets colder. Do you know how to access and use the controls for the boiler?

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I’ve got the instruction manual so would be happy to look at the controls. The flow temp is set at 85°C, which the installers set, I’ve just checked.

 

[gmartine]

I meant too high sorry and yes that's far too high so return temp will be too high hence the anti-cycling, make a note of return temp (A1) and delta T (A3), instruction shown in previous post. Do you have weather comp and therefore an outside sensor (A5)? Even if boiler set at delta T 25 the boiler is operating outside condensing mode so something amiss here.

 

[Jonny]

I meant too high sorry and yes that's far too high so return temp will be too high hence the anti-cycling, make a note of return temp (A1) and delta T (A3), instruction shown in previous post. Do you have weather comp and therefore an outside sensor (A5)? Even if boiler set at delta T 25 the boiler is operating outside condensing mode so something amiss here.

Ok so I’ve written down those values at the end of the ‘burner on’ cycle for a few cycles, A0 is always 64°C, A1 is always 33°C and A3 is always 58°C, there is no A5. So clearly the flow and return temps are very different, and are nowhere near the set 85°C
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Just an update, the boiler seems to have started working properly again, with A0 85°C, A1 59°C and A3 83°C. This coincides with the hot water coming on at 4pm, and thinking back this was the pattern last year as well. However it is still a problem during the day, so could this suggest a problem with the automatic zone valves?

 

[gmartine]

Are you saying that when the hot water program is enabled (cylinder, 2x day?) the CH gets up to the desired temperature and the boiler no longer seamingly anti-cycles?

 

[ShaunCorbs]

Do you have weather comp ?

 

[Jonny]

I think that might be the case as when the hot water comes on in the evenings the central heating begins to work properly at this time, however when the hot water cylinder stat isn’t calling for hot water and there is only a call for central heating the boiler goes back to not working correctly. This evening the HW came on and the boiler ran for a long time, CH was very hot, but when the water was heated fully, CH no longer works properly until there is another call for HW
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Do you have weather comp ?

No I don’t think so, as when I pressed the A5 button (the button for external sensor) the display read ‘ - - ‘

 

[gmartine]

The flow temp is exceeded when CH is on only that's why the anti-cycling kicks in but it all seems to works fine when the HW cylinder comes on.

That suggests to me that the water is returning too hot so it isn't expended properly in a balanced system and or it's also too hot to begin with. Don't know what flow set T is on the ATAG, thought it was delta T but cant be looking at your numbers. Describe your system/settings etc.

 

[Jonny]

The flow temp is exceeded when CH is on only that's why the anti-cycling kicks in but it all seems to works fine when the HW cylinder comes on.

That suggests to me that the water is returning too hot so it isn't expended properly in a balanced system and or it's also too hot to begin with. Don't know what flow set T is on the ATAG, thought it was delta T but cant be looking at your numbers. Describe your system/settings etc.

I’ll try to describe it as best as I can, don’t know the proper names for some things so bear with me. Starting with the boiler, the CH water temp is set at 85°C. The hot water goes to the airing cupboard where there is a circulation pump (set at the fastest speed) and two automatic valves, for CH and HW. The CH is set to constantly on and is controlled by the room stat, which is definitely working correctly, and the HW is controlled by a horseman programmer under the boiler. It is set to come on in the morning and evening, and the hot water temp is set quite high on the cylinder stat. The cylinder is a megaflo. There is also a header tank in the attic which just has a feed down into the boiler circuit, to top it up in case any water is lost
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I’ll try to describe it as best as I can, don’t know the proper names for some things so bear with me. Starting with the boiler, the CH water temp is set at 85°C. The hot water goes to the airing cupboard where there is a circulation pump (set at the fastest speed) and two automatic valves, for CH and HW. The CH is set to constantly on and is controlled by the room stat, which is definitely working correctly, and the HW is controlled by a horseman programmer under the boiler. It is set to come on in the morning and evening, and the hot water temp is set quite high on the cylinder stat. The cylinder is a megaflo. There is also a header tank in the attic which just has a feed down into the boiler circuit, to top it up in case any water is lost

Also I have never seen the return temp on the boiler higher than the flow temp.

 

[gmartine]

What's your radiator circuit like, how many, do they have TRV's, what are they set at, has it ever been balanced, do they all not heat up properly?

Where is your room stat, is it in a room with a rad with a TRV? Is it in a vulnerable postion in terms of exposure to heat, cold, draft or sunlight?

 

[Jonny]

What's your radiator circuit like, how many, do they have TRV's, what are they set at, has it ever been balanced, do they all not heat up properly?

Where is your room stat, is it in a room with a rad with a TRV? Is it in a vulnerable postion in terms of exposure to heat, cold, draft or sunlight?

There are 13 radiators total of varying sizes, all have TRVs apart from one in the downstairs hallway where the room stat is and the towel rails in the bathrooms. All downstairs TRVs are set to maximum, and 4 of the upstairs ones (in bedrooms) are set about halfway. I believe it is balanced, the valves on the upstairs radiators are only open a quarter turn, while the downstairs ones are open a bit more- this is what the installers of the boiler suggested.
Heating circuit is plumbed in 22mm speedfit (all in ceiling, nothing under downstairs floor) with 10mm speedfit legs going off to radiators. As a result upstairs radiators get a bit hotter than downstairs radiators (poor design?) as the 10mm speedfit run to them is shorter and some downstairs radiators get hotter than others depending on length of speedfit run.
However all the radiators are still affected by this boiler problem.
So room stat in hallway, and no TRV on hallway radiator, isn’t in sun or particularly exposed to extreme temperatures.

 

[gmartine]

Make a note of the TRV and lockshield settings of all your rads (should you wish to return them to your installers setup) then fully open them (both ends) and just see if they get up to full temp without your boiler anti-cycling.

 

[Jonny]

Update:
Just to complicate this further, the boiler and CH seem to have been working fine today.
Whereas yesterday the CH would only work when the hot water was on.
The only difference between these two days is that yesterday it was much colder outside (0-2°C) and today it has been a bit warmer (3-5°C), the timings for the CH or Hw have not changed at all.
I can see that this would make sense if there was a malfunctioning weather sensor, but as I said earlier when I press the A5 button on the boiler (the button for outside sensor) the display reads ‘ - -‘ which I took to mean there is no sensor. Am I correct in believing there is no sensor, and any ideas why the outside temperature is affecting the boiler?

 

[gmartine]

It thought we established there's no weather comp/sensor earlier.

When it's colder, there's more demand on your system to get up to temperature but I believe because of the inherent restrictions in your radiator circuit...10mm branches plus all the trimming on each radiator the return flow temp is too high so the anti-cycling kicks in and so your system never quite gets up to full temp. Try what I recommended in #13, it costs nothing but a bit of time.

 

[Jonny]

It thought we established there's no weather comp/sensor earlier.

When it's colder, there's more demand on your system to get up to temperature but I believe because of the inherent restrictions in your radiator circuit...10mm branches plus all the trimming on each radiator the return flow temp is too high so the anti-cycling kicks in and so your system never quite gets up to full temp. Try what I recommended in #13, it costs nothing but a bit of time.

Ok I will try that the next time it starts anti-cycling (probably tomorrow), and report back, thank you for your help so far

 

[gmartine]

You're welcome...the other reason I think it may be your radiator circuitry is that you reported the CH works fine when the HW is also on, in other words the extra load appears to prevent the boiler from anti-cycling. If it doesn't prove to be that we can always try altering some settings but I assume some of your previous engineers/enquiries took you down that road.

 

[Jonny]

You're welcome...the other reason I think it may be your radiator circuitry is that you reported the CH works fine when the HW is also on, in other words the extra load appears to prevent the boiler from anti-cycling. If it doesn't prove to be that we can always try altering some settings but I assume some of your previous engineers/enquiries took you down that road.

You're welcome...the other reason I think it may be your radiator circuitry is that you reported the CH works fine when the HW is also on, in other words the extra load appears to prevent the boiler from anti-cycling. If it doesn't prove to be that we can always try altering some settings but I assume some of your previous engineers/enquiries took you down that road.

Today I tried turning all the TRVs and almost closed lockshields up (all while hot water was turned off) and the boiler and CH worked properly. However the boiler and CH also worked properly (with HW off) when the lockshields and TRVs were in their original positions. I’ve only had a chance to try this in the morning and evening as I’m away during the day, but I can try again in the weekend. The other difference today is that it was warmer outside again (5-7°C).
I’m not discounting the theory that the problem is caused by the number of closed lockshields and TRVs, but this hasn’t caused problems unless it’s been cold outside, so the cold temperature outside definitely seems to be the cause, somehow.

 

[gmartine]

The extra demand or load IS caused by the decrease in temperature, I don't know how else to describe it to you. I asked you to fully OPEN the lockshields not nearly close them. Good luck, I'm out.

 

[Jonny]

The extra demand or load IS caused by the decrease in temperature, I don't know how else to describe it to you. I asked you to fully OPEN the lockshields not nearly close them. Good luck, I'm out.

Sorry, I can see how my post was confusing, I meant that I fully opened the lockshields and TRVs that were previously nearly closed. Anyway i will try this again the next time the boiler starts anti-cycling, as today it seemingly worked fine with lockshields and TRVs closed or open.
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The extra demand or load IS caused by the decrease in temperature, I don't know how else to describe it to you. I asked you to fully OPEN the lockshields not nearly close them. Good luck, I'm out.

Can totally understand if you’d rather not keep helping and advising for free, but if anyone could it would be greatly appreciated, as the company that installed the boiler are struggling to solve the problem.