Potterton Profile 50e switches on then off again

[redharry123]

Hope someone can help. My 23 year old boiler has developed a fault. It usually (but not always) switches on O.K through the timer and starts heating up water and rads, then after about 15 minutes switches off and does not come back on. I can reignite it via the little button at the bottom the boiler unit and it seems to then work O.K. Same issue if I put the boiler on via the 1 hour advance buttons on the timer box.
Does not seem to matter if it is just hot water, just rads or both.

I have changed the timer control unit with a borrowed one from a plumber mate but the problem continues.
Any thoughts before I call someone in.
Thanks for your help .

 

[picasso]

The "little button" on the bottom of your boiler is the overheat stat reset button, it may be a circulation problem (pump) or pump over run stat faulty, these are very basic boilers so it shouldent be difficult finding someone to repair it.

 

[scoobydo123]

If it is the overrun stat you can get round this by wiring in a timer relay (to the pump. That way you do not need to open the casing. I have done this on my boiler and never had a single trip since.

When the burner switches off do you hear the pump continue to run? Can probably simulate the fault by letting it heat the HW cylinder wait for the boiler to cycle at least once then let it heat again and then stop call for heat on cylinder stat (by turning down). If the boiler is up to a decent temp then you should hear the pump continue to run, if it doesnt then you will probably hear the overheat stat click.

 

[Steelmasons]

Possibly boiler stat out of calibration so tripping overheat or vice versa , normally change both stats , if boiler OH stat is tripping whilst burner still alight then most certainly a thermostat issue.

 

[bathjobby]

I had same problem some years ago with same boiler. Had worked fine for about 20 years with just the very odd boiler overheat stat tripping in harsh winters. Then got that symptoms most of the time. Turned out the boiler had never been wired to overrun even though it is capable of being wired this way; i.e. when flame went out, pump was switched off, hot water (not being circulated until it had cooled) in boiler tripped the overheat stat. Turned out the whole estate was wired this way - cowboy plumber / sparky sub-contractors; unless the builder specified it this way to save money !
Are you on an estate in the South ?

As Scooby said above; does the pump continue to run after the boiler flame goes out prior to the stat tripping ?

 

[cbiscuit]

I had this once with a Profile 60, it would never display the problem when I attended but would randomly trip off. Fully tested and no problems or installation issues. In the end I replaced the pcb and that sorted it, no idea why though!

 

[bathjobby]

The PCBs in these boilers are also renowned for problems (web / DIYNOT search). Same boiler, I developed a noisy fluttering gas valve. Huge (obviouse to the eye) dry joint on gas valve circuit. Digressing though; I guess he needs to check for pump overrun 1st for his symptoms.

 

[redharry123]

Thanks everyone for the quick replies.
Will do some checks on the pump as suggested.
Bathjobby, the house is on an estate in the South (Dorset) and the builder went bust after selling the last one !!! Possibly skimping a bit to save cash - I have learnt a lot about plumbing while in this house !!

 

[Tipper]

Mine had the same symptoms, it was the pump that had failed. At first intermittently then completely.