Combi boiler cuts out and wont re-fire

michelle2010 · 10 Mar 2010

I really help someone can help.
I have an Ideal combi boiler and it fires up ok until it hits temperature and cuts off, it then wont refire up until I switch it off and on again (sometimes I need to switch it off up to 3 times before it will fire up). The boiler still runs (I can hear everything running as normal) but it just wont heat up. I do not have an external thermostat. The pressure gauge reduces back to normal and it does not matter how cold the rom gets or for how long the boiler just wont refire until it has been switched off. It also wont fire for water at this point.
I have had engineers out and noone seems to know the problem. Any suggestions that I can give them would be greatly appreciated.
I am no expert with boilers so if you can answer in very simple terms I would appreciate it.
Thanks

Gasman28 · 10 Mar 2010

I'm guessing it's an Isar?
When the boiler shuts off, do you get any fault codes on the display unit?

Andygasman2010 · 10 Mar 2010

need more boiler details really...

michelle2010 · 10 Mar 2010

No I dont get any faults showing up (though there isnt a digital display). The pressure appears ok (between 0.5 and 1.0 when off, going up to about 2 - 2.5 when hot then it does go back down gradually when the boiler cuts off).
I also had it desuldged recently because I was told that might be the problem but it hasnt improved.
What other info do you need?
BTW it's an IDeal Combi Boiler model CF88

Andygasman2010 · 10 Mar 2010

firstly, that's quite a large pressure fluctuation. You probably need your expansion vessel recharging. How many rads are on the system? I doubt this would be causing the problem you're describing though as this boiler doesn't have a pressure sensor, only a primary flow switch. Anyway, there could be alsorts causing the fault you've described. I'd suspect the ignition PCB but it could be several other things. Without experiencing the fault and doing a few checks it's very difficult to say, especially on here. I'd recomend getting an RGI out to experience the fault and do some checks. Hope that helps!

jackecole · 10 Mar 2010

Andygasman - do you mean due to TRv's possibly closing down/bypass wrongly set or all rads having trv's - the system pressure may get too high and cause boiler to lockout? This could happen without a pressure switch I believe?

The fault code be a pump or fan overrun fault, the pump could be failing/slowing down, or even there could be sludge in the main heat exchanger that only causes an overheat/boiler to lockout when the circulation stops (ie demand satisfied)

Andygasman2010 · 10 Mar 2010

jackcole

it's all a bit vague though really, it's all to speculative without actually seeing the fault or doing any checks. if the pressure was to get too high it should just relieve out of the PRV, there are no sensors to tell the board the pressure is to high. only a flow swicth which wouldn't make if the pressure was too low. it doesn't sound like that's happening here though. It could be any of the things you're mentioned there, although if it was actually getting too hot i would expect it to fire up again and apparently it doesn't

not sure what you mean about the TRV's/bypass thing you meantioned... if all trv's were closed the pressure wouldn't increase anyway

jackecole · 10 Mar 2010

I agree - what I mean was if say the system had all TRv's fotted or the bypass set too low and the system pressure increased when trv's closed, then the boiler would overheat and go to lockout and need re-setting, mainyl due to the heat from the boiler not being got rid off due to rads being closed off after a while. but again the pressure would build up and possibly cause the prv to blow (if the boiler didn't lockout first)

as you say it's speculative without seeing. Do you think boiler fault finding is easier in real life than on here !!?

anyway: even without a pressure switch - the pressure if got to 3 bar (due to overheating/expansion etc) - prv would blow

Andygasman2010 · 10 Mar 2010

jackecole said:
I agree - what I mean was if say the system had all TRv's fotted or the bypass set too low and the system pressure increased when trv's closed, then the boiler would overheat and go to lockout and need re-setting, mainyl due to the heat from the boiler not being got rid off due to rads being closed off after a while. but again the pressure would build up and possibly cause the prv to blow (if the boiler didn't lockout first)

as you say it's speculative without seeing. Do you think boiler fault finding is easier in real life than on here !!?

yea sure it is

if either of us could see this fault in action, i think we'd sort it in no time

why would system pressure increase when trv's shut down? i don't see how that could effect system pressure?

Andygasman2010 · 10 Mar 2010

ah i see what you mean now. like i said earlier, if it was getting too hot it'd fire back up again when it cooled down. apparently it doesn't. and i don't think he mentioned anything about reseting a manual overheat stat did he?

jackecole · 10 Mar 2010

Andy- the poster said they turn the boiler off/back on again - so I presume to reset it.

if the trv's all close, the system pressure builds up and the overheat stat may well trip due to increased pressure/temperature. So water too hot and oerheat tripped, not just boiler stat cycling on/off etc. Prv could even blow.

Andy: do you do boiler repairs? Have you been to any manufacturer courses?

Andygasman2010 · 11 Mar 2010

Yep, i'm an experienced heating engineer.

This boiler doesn't work like that, it has a manually resetable overheat stat so if it overheated he wouldn't be able to simply turn it off and on again. Also, as i've said before, trv's or bypass being closed wouldn't make the pressure increase, only the temperature. Even then it would only overheat and apparently it's not. If it was getting too hot and the primary sensor was cutting it out, it'd refire after cooling down. Sounds more like a board problem to me, it has a CVI ignition board on the gas valve, i've had to change plenty of them before. It'd be nice to know exactly what's happening when it's cut out I.E. are the fan and pump still running? if they are i'd check fan/aps/venturi etc... if they're ok go for that ignition board

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Combi boiler cuts out and wont re-fire

Similar threads