Boiler stat on/off temperatures

[Bandy]

Hi
I have a problem with my Potterton Prima F gas boiler. The overheat stat pops out almost daily. I have turned the boiler stat down to almost off and it still happens. I ran the heating this morning and measured the flow temp from the boiler. It got to 82 c before the boiler stat shut down the boiler and after cooling it fired back up again when the flow pipe temp was 38c.

After firing for this second time, the boiler flow pipe temp reached 84c before the boiler stat shut it off. There was no overheat stat pop out however.

I then turned the boiler stat up to 2 and the flow reached 84c before the boiler stat shut the boiler off again. It then fired up at 55c. I kept measuring the flow pipe temp, it got to 84c and the overheat stat popped out.

So the boiler stat setting seems only to affect the firing temp and not the final temp. Is this the way these thermostats usually operate? And is 84c too close to the overheat stat trip temperature? I appreciate the overheat stat measures the temperature of the boiler and not the water but I would have thought that turning the boiler stat down would lower the temperature at which it shut the boiler off and avoid these nuisance trips.

Any advice would be appreciated.. If any more info is needed, just ask.

 

[Bandy]

Sorted. The boiler thermostat bulb was not clipped to the flow pipe inside the boiler casing. It was waving in the breeze about half an inch from the pipe so it was picking up radiant heat from the pipe and should have been in direct contact. If you have the same problem, have this checked first. It needs to clip back on with some heat sink compound to make sure the stat bulb is properly picking up heat from the pipe. The nuisance tripping of the overheat stat has plagued me for years and it was such a simple fix. I am one happy bunny right now.