I have a 25 year old Baxi boiler, which is generally ok, except-when the timer switches on, the boiler doesn't always fire up, although the pump is running. However, if I turn the boiler thermostat knob off, and then back on again, it fires up no problem. There are no othe thermostats in the house, boiler uses a constantly on pilot light.-Big problem or not??

Might just be an overheat stat.....the action of turning off/on probably resets it and away you go. Not a major problem but you need to know why. Circulation problem is cause of most overheats......either pump is struggling/system is sludged/no pump over-run/no bye-pass open etc etc. I assume its a conventional boiler and if you post the exact make and model it may help more. I am sure the other lads on here will be able to shine some light on this too, cheers
Steve

Thanks for that, boiler is a conventional Baxi WM 381RS, I am not really clued up on boilers, but as it sometimes wont fire up in a morning when it is cold, I cannot see why its an overheat problem?? Once it starts up, its fine!!!!

Yes, 'once it starts it's fine', which is why overheat could be the problem, if, for instance, when the boiler shuts off the pump does not over-run then the heat will stay in the boiler and cause it to overheat...hence next time it is due to fire up then it does not cos it has 'locked-out' on overheat, and you need to reset it and it is ok again. This is just a guess at the moment but it seems to make sense without further investigation,
Steve

Yes, 'once it starts it's fine', which is why overheat could be the problem, if, for instance, when the boiler shuts off the pump does not over-run then the heat will stay in the boiler and cause it to overheat...hence next time it is due to fire up then it does not cos it has 'locked-out' on overheat, and you need to reset it and it is ok again. This is just a guess at the moment but it seems to make sense without further investigation,
Steve

Thanks, I think I'll drain and refill the system, the water is a bit (lot) black looking!! . How does heat escape from the boiler when it shuts down after being set t hot water only, ie, pump not running? .Thanks again, I'l let u know what happens.

Thanks, I think I'll drain and refill the system, the water is a bit (lot) black looking!! . How does heat escape from the boiler when it shuts down after being set t hot water only, ie, pump not running? .Thanks again, I'l let u know what happens.

I,ve just found the boiler thread!!

if it was me I would add some fernox central heating restorer then leave it for a couple off days then drain down. (it will break all the black muck up) the add at least 2 litres of inhibitor when re filling. good luck

if it was me I would add some fernox central heating restorer then leave it for a couple off days then drain down. (it will break all the black muck up) the add at least 2 litres of inhibitor when re filling. good luck

Thanks, will I have to drain the system slightly ,or just pour the Fernox in??

yeah drain a couple of buckets off should be fine

if it was me I would add some fernox central heating restorer then leave it for a couple off days then drain down. (it will break all the black muck up) the add at least 2 litres of inhibitor when re filling. good luck

Sorry to be a pain, I've seen fernox f3 and fernox f3 heavy duty on ebay, (500ml)heavy duty is £10 +p&p-does this sound ok. thanks-how much for an up to date system fitted.??-I think its about knackered, But should qualify for scrappage.Thanks again.

Sorry to be a pain, I've seen fernox f3 and fernox f3 heavy duty on ebay, (500ml)heavy duty is £10 +p&p-does this sound ok. thanks-how much for an up to date system fitted.??-I think its about knackered, But should qualify for scrappage.Thanks again.

Yeah that sounds ok. For a new system I would need to come and see you to do a quote please call me to arrange.

Yeah that sounds ok. For a new system I would need to come and see you to do a quote please call me to arrange.

Thsanks, will do, we live at Shirecliffe.