Potterton Promax 15HE cutting out

Hi all and apologies if this question has been raised before but...
I have a Potty Promax 15HE boiler that is about 8 years old and has been fine but recently its been cutting out and usually fires up again once the reset switch is flicked.
Today, i flicked the switch but it wouldn't ignite, it just clicked a few times then shut down.
After i'd been out and came back again the heating was on as the wife had flicked the switch and it worked for her. (dammit!)
So i took the cover off and checked the Condensate trap which was full as there must be a prob somewhere.
I removed and cleaned alot of sludgy stuff and re-fitted it all, switched on and the boiler fired up ok.
My question is, The right side of the trap filled up which i assume is right(?) and the left side only filled a wee bit then seemed to stop. Is this correct? Does the right side remain full all the time and continues to overflow to the left side? Why does it need to fill to this point and not just drain straight to the pipe? Would this have been the cause of the cutting out? I don't know if it had ever been emptied before so i'm hoping its the cause. It has gas and doesn't appear to be overheating so fingers crossed.
Many thanks guys and gals.

IME if it was a blocked condensate trap, the boiler would behave like there was a fault with the flame sensing electrode (i.e. fire up then shut down, repeat x 4, then lockout). The trap is designed to empty in one hit as this makes it less prone to freezing in the outlet pipe.
Does it cut out when the heating/HW is still calling for heat? If so it could be the combustion box door seals. If it first lights up with a big 'whump' then that's an indicator of failed seals. A failed seal allows combustion gases to leak into the inner case and when it gets hot enough in there, the fan protection stat trips and shuts down the boiler. Once it cools down enough, the stat resets and the boiler will fire up again.
Do you have a multimeter? You need to check if any of the safety switches are tripping (fan protection stat, overheat stat, flow switch) and also the resistance of the flow thermistor. This will give you an idea of what's wrong.

Thanks for the reply.
Its tripped out again at some point and at the moment won't restart. After flicking the reset switch the fan starts, something in the black box clicks twice but it doesn't ignite. It does this 4 times then the fan cuts off and its powered off.
I'll try again in a while when everythings cooled off a bit and see if it fires up.
Yes it trips while calling for CH/HW.
And yes, i do have a multimeter so i'll test the parts you mentioned tomorrow with a bit more light.
Can the thermistors just be left in place and tested? I'm assuming i just need to remove the connectors/spade terminals and bridge the gaps or do they need to be unscrewed to test them?

If it were the condensate trap, it would be lighting and then shutting down, so I don't think it's the trap sensor.
If the fan's coming on then the safety cutouts would seem to be working OK. You can test them for completeness if you wish!
As it's trying to ignite (going through 5 ignition cycles) then it's likely there's either a problem with the ignition board/spark electrode or it's not getting gas. Have the electrodes been replaced recently? If not, I would suspect these first, then the ignition PCB.

Thanks for the reply.
Found all my thermostats etc to be good, the combustion door seal was crumbly and a small part was missing which has been replaced now.
As far as i know the electrodes have never been replaced so i'll do this as they are so cheap and easy to do.
Other than that the PCB would be the only other thing.
I while back i removed the board and re-soldered a pin cos it was arcing on one of the ignition pins due to a bad solder joint. I could hear it sparking even with the cover on, but a quick blob of solder and it has been fine ever since. Hmmm, obviously not the best PCB in the first place so yes, as you say it'll probably be down to this.
Thanks.

Got my boiler sorted.
The ignition PCB (which i had soldered before on the ignition pin) had a transistor which had some very slight browning round the pins like it had got too hot, closer inspection revealed poor and pitted solder around the pins so i resoldered it and so far all is well, boiler does what its supposed to and turns off at temperature instead of cutting out at random points.
Went over most of the solder points while i was at it too as these boards are obviously cheapo bits of kit with dodgy solder in the first place. Definately not worth the price they charge you for a new one.
Cleaned it out and gave it a mini service while i was at it.
So if anyone has a boiler with cutting out/ignition probs and the obvious are counted out it might be worth checking out the PCB for weak solder.
Yeah, i know i could have just fitted a new one, but i'm a skin flint and refuse to shell out on what i can fix myself!
Cheers to all for their advice!

bernardbeemer said:

Got my boiler sorted.
The ignition PCB (which i had soldered before on the ignition pin) had a transistor which had some very slight browning round the pins like it had got too hot, closer inspection revealed poor and pitted solder around the pins so i resoldered it and so far all is well, boiler does what its supposed to and turns off at temperature instead of cutting out at random points.
Went over most of the solder points while i was at it too as these boards are obviously cheapo bits of kit with dodgy solder in the first place. Definately not worth the price they charge you for a new one.
Cleaned it out and gave it a mini service while i was at it.
So if anyone has a boiler with cutting out/ignition probs and the obvious are counted out it might be worth checking out the PCB for weak solder.
Yeah, i know i could have just fitted a new one, but i'm a skin flint and refuse to shell out on what i can fix myself!
Cheers to all for their advice!

Click to expand...

Thanks for your posts. Hade same problems with the ignition. Took out the ignition pcb found a dry solder stuck a blob on... all sorted. Thanks again.