Atag boiler only cycling on for a short time

[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.