Odd reset problem with a Potterton profile 100e

[discostewart]

Hi,

I have a SIME badged Potterton profile 100e.

Every morning as my electronic Programmer switches off the boiler therm stat reset button trips and i have to go down and reset it. (The button under the boiler). It basically does it aswell with +1hr or turning the water off manually,

We have replaced the overheat stat and the pump over run stat. We also found the gas supply has been set to the wrong flow and altered it. Neither over these things has changed the problem. The ONLY thing that alters is it very odd. If you change the stat on the hot water cylinder in the bathroom down to 50 it doesnt reset! Im not sure why altering the temp of cylinder would affect the boiler.

it does not reset on the central heating.

Am at a total loss as r two corgi guys helping me.
;(
Stewart

 

[sonray ltd]

change the cyl stat.

 

[plumberdate]

is there a motorised valve on the sytem? may look sumert like this??

Motorised Valves - DIYWiki

 

[discostewart]

Plumberdate:
there are what appears to be two motorised valves

honeywel f4 9933
honeywell f9 9923
both in airing cupboard.
system is fully pumped.

Sonray Ltd:
happy to change cylinder stat but why would that cause the boiler to manually reset downstairs ?

Im a layman so excuse my question but the temp of the cylinder shouldnt overheat the boiler ? Its trippng at the end of the cycle not during ? (ie when the boiler turns off as HW goes off at end of programme). This morning however it didn't cut off because last night i altered the stat down from 65 to 60. Which kind of fixes it but only in a bodge sense and i want to sort it properly. My corgi guy doesn't seem to think it would be the stat/valve.

 

[plumberdate]

hiya, it could be soo many things without being ther its hard to tell.

beings as when u mess with the cylinder stat, seems to point to some sort of overheating. if one of the motorised valves has broke it could be that the hot water is over heating as both hot water and heating will be on at the same time (when you select central heating on programmer - does hw come on aswell)

hard to tell, but its looking like overheating from the info supplied so far

 

[discostewart]

The hot water button doesn't come on the programmer when your CH does. And i would say it isn't heating both at same time as water cold in evening when CH is on and HW program is off. But i will check that tonight.

I agree its overheating but could a cylinder stat cause that ? the overheat stat and pump overun stat have been changed to no affect.

 

[Deleted member 2053]

If you have two motorised valves do you also have a bypass? If both valves shut with no bypass then there is nowhere for the pump overrun to pump to and the residual heat in the heat exchanger could be enough to trip the overheat. It is just possible then that reducing the cyl stat will reduce the return temp so the residual heat does not raise the water enough to hit the overheat. Easy to test - just hold one of the motorised valves open very slightly (not enough to activate the microswitch) as you turn the power off. If it doesn't trip then you have your answer.

 

[discostewart]

there does indeed to appear to be a bypass. the only odd behaviour we can find is the pump override. it seems to kick in on the central heating most of the time but not with the hot water. ie it only runs after central heating has shut down. bypass appears open, pump operational so not sure why its intermittent, as the signal should be either on or off.

 

[Deleted member 2053]

Well that would certainly fit a little better with the fact that you can stop the overheat with the cyl stat. Start by unclipping the programmer from the wall and then check that you really do have a permanent live to the boiler.
This is a long shot but I did once come across a situation with a profile where someone had rewired the boiler internally because he couldn't work out how to correct his faulty exteral wiring. That coupled with some external wiring error would give you this result. I know much better plumbers than I who are the most appalling electricians. Profiles always used to have a colour coded wiring diagram on the inside of the undertray.

 

[discostewart]

Plumber has checked permanent live is there. Another plumber verified it. Also the fact the pump overides when central heating shuts down would suggest something is in place?

do u think changing the cylinder stat would have any bearing on this? i dont understand how it would ?