Halstead Finest Gold combi probs

[houseisbig]

I am having problems with my Halstead boiler and wonder if anyone can give me some advice.
Initially my boiler would not respond to being turned off at the boiler clock, and continued to provide heating unless turned off at the mains.
On starting the boiler at the mains with the clock switch set to off the boiler starts up and provides CH. The boiler does not seem to run long before it stops, radiators are warm but not hot. Boiler then continues to come on and off even if you turn off or on or timed on the clock or if the stat is off or on or the link is in for "no room stat".
I have 240v across the live and room stat and it turns to 0v when stat turned off. I have also swapped the thermistors so the DHW and CH ones are swapped and this makes no difference. The DHW is fine.
I have also moved the "no Clock jumper on the PCB but this makes no odds. The fan venturi and flow Diaphram are ok.
I know the boiler has a frost protection on it and wonder if this is any way causing the prob? Please help

 

[gas4you]

Check any motorised valves have not stuck open, or the head micro switch hasn't broken on.

 

[Gasguru]

Look at the switch box on the left hand end of the diverter valve. Perhaps the diverter pin is partially siezed (ie pin is out) switching on the hot water despite there being no demand.

Or check the microswitch has not failed to short circuit.

 

[ChrisR]

Um Dave - it's a combi
ANy frost stat is likely to be operated through the ch sensor, so yo wold apparently have eliminated that.

Check the flow switch which is in the transparent box on the left hand end of the brass diverter. I'm thinking maybe the switch is not switching cleanly resistance wise, and the diverter itself is stuck part open.

 

[gas4you]

Check any motorised valves have not stuck open, or the head micro switch hasn't broken on.

what a d i c k head, just saw Halstead and not combi

 

[superdupergasman]

Does this boiler use the Primary sensor for frost protection??

Is it sited in a cold spot...it is cold just now so might be just keeping itself warm...or does it have an external frost/pipe stat??

 

[houseisbig]

The boiler is in a cupboard under the stairs so not prown to cold.
I will check the diverter pin but would that cause the boiler to start even when in the off position?

 

[ChrisR]

If the switch is on, the boiler would think the hw is on, but it isn't so the rads would warm up. The pin could be stuck and operating the pin.
If the gland seal leaks, water gets in the switch and does this sort of thing.

 

[houseisbig]

Just checked the switch and found the contact switch wet with water!
I will dry it out and see what hapens

 

[scatmanjohn]

If its wet, you have a leak from the end of the diverter.

Diverter service kit should sort things.

 

[houseisbig]

Stripped switch down, cleaned contacts and dried out, re-fitted and things back on track. I have had this problem for quite some time and had the hassle of turning the boiler off at the mains every day, hopefully i can use the timer and room stat once more.
I am so very grateful to you all for your swift response and successful help.
Having a Halstead boiler i am sure i will be back for advice again