Combi boiler cycling.

[Jimboben724]

Hi,

I have a Ravenheat White Star LS100 about 15 years old. No room stat but TRVs.

Recently it would not fire and the PCB was replaced and a boiler leak fixed. The boiler now runs for 10/15 minutes then starts cycling 30 seconds on/off.

I have tried adjusting the rads and the pump speed to no avail. When I set the pump to 1 the pressure guage needle jumped about.

I have spoken to a couple Gas Safe engineers and one mentioned removing a jumper on the board but he could never make time to come round to do it.

What puzzles me is everything was working fine until the PCB failed and was replaced but this fault has appeared.

I would appreciate any suggestions to resolve the problem.

 

[ianmcd]

how many radiators do you have

 

[Agile]

It could be that the boiler power output is too high for the number of rads you have turned on and it is just cycling on temperature.

You do not say who replaced the PCB but any RGI would check the power output to ensure that it matches the heat load.

It is quite likely the PCB has a CH heat output adjustment setting and these are sometimes ( wrongly ) supplied set at max on the assumption they are to be fitted by a qualified person who will fit them professionally.

It was never a very popular boiler and I doubt there are many left now. It has an annoyingly non standard diverter valve and those are the cause of most of the faults I have needed to fix on that model.

 

[Jimboben724]

Hi Ian,
There are 3 rads on the ground floor and 4 on the first floor.

 

[ianmcd]

Only thing on the new PCB that is different is as already advised it could be now set at max and the boiler cant get the overload of heat out, it needs to be set by a gas registered engineer, it is not a DIY task, not a hard task but you need the equipment to do it

 

[Jimboben724]

Hi Agile,
Thanks for the rapid reply.
I didn't see any adjustment being made when PCB was fitted. Looking at the old PCB, there only appears to be one adjustment point which I think is a potentiometer. I have spoken to 2 GSEs and only one mentioned removing a jumper( whatever that is). The other didn't talk about any adjustment.
As a layman, I thought the diverter valve directed the heat to the rads or the DHW. The DHW is working satisfactorily.

 

[Jimboben724]

Thanks Ian.
My next question is - Is there a GSE on this forum, convenient for Stockport, who wants to do the job?

 

[Jimboben724]

Thanks for your help Ian.
The potentiometer didn't solve it so I called Ravenheat tech support and after explaining the situation was advised to fit a room stat.
I have now done this and although the boiler still cycles the time is greatly reduced. Also the boiler and pump shut down for periods.