Lock Out Problem - Potterton Kingfisher Mf RSL 80

[MarianH]

Timer set to "Water Only - Twice a day". Boiler turns on but it appear thermostat does not work and the boiler "trips out", Red light comes on. Reset, same thing happens. Two separate engineers called, changed pump and two parts inside boiler (Thermostat I think). Problem solved - but after a week same problem has returned. Have noted that if the Heating and water are turned on together for a short time, the boiler does not "trip out", then after 15 minutes you can turn the heating off (leaving water only ON) and the boiler works (no trip out) until it turns off at the timer at the end of the period say night time. However when the boiler turns on again in the morning (water only) the same problem occurs, it trips out. Then same process can be gone through as above. Engineers appear puzzled, costing me money in call outs and part - ANY possible causes/solutions would be most welcome - thank you.

 

[45yearsagasman]

It does sound like a temp related issue, either poor initial circulation or maybe overheat tripping intermittently.
Very difficult to diagnose these sort of faults without being in front of boiler with test gear and following the fault finding charts to determine at what stage the lockout occurs.
Discount the pump as its new and is probably ok. Having said that, a new pump won't overcome blockages in your system, which would give you similar symptoms.

 

[MarianH]

Mr "Gas Man" - can I thank you for your speedy reply. I will ask an engineer to look at the potential cause as you describe.