Vokera Compact HE 25 - Fire Up few seconds, then off, then repeat

[Moi]

Hi

I have a Vokera Compact HE 25 which is exhibiting a strange issue in that when it fires up which it does quite readily, its flame goes on and its on for perhaps 2-3 seconds then goes off again for 2-3 seconds, then fires again, repeat endlessly. All the time the green light is flashing 0.5secs on/off so it doesn't go into lock out/red light at all.

After perhaps 10mins of this when CH called for, it seems to work better and stay fired up for longer periods and the CH does get hot and if I call for HW when its like this WH is fine and hot, if I call for HW when the boiler isn't performing CH duties and constant burn, all I get is luke warm water.

I've replaced the 2 thermistors to no avail (the old ones tested ok on multimeter), drained the system, added cleaning agent for a few days, then drained again and refilled including inhibitor although I'm confident I don't have any blockages or sludge as the drained water from the initial draining was crystal clear and bleeding radiators also only give clear water (no rust/sludge etc).

The last thing I've tried is a 'new' Ignition Module but fitting this results in the boiler failing to fire and locking out totally. The seller said this was due to the gas needing recalibrating for a new PCB but I'm not sure I believe that as solid state PCB's should give consistent voltages/timings etc and suspect I've been sold one pulled from an old system and possibly more faulty then perhaps my current ignition board is (if it is this board).

I have BG coming monday as I know I'm limited on what I can do to try fix (limited to electrical side/component swap outs.....staying clear of direct gas components) but has anyone ever seem this sort of thing before on a Vokera as its difficult timing showers/washing up when the water runs luke warm unless the CH has been on and heating for 10mins or so when the boiler then seems to function normally?

 

[CBW]

Hello,

I take it you’re not gas safe registered with BG attending on Monday? You have worked on a gas burning appliance, and you mention staying away from gas components, yet have replaced the ignition module? My advice is to wait for BG to attend on Monday.

Thanks.

 

[Moi]

The ignition module is 100% electrical and I've checked and I don't have to be gas safe registered to swap like for like electrical (or water only bearing) components on my own boiler if its not for profit (being paid). I understand your concern but I'm competent with electrics, have another ignition module arriving soon and if swapping that out doesn't fix it I'll await BS engineer on Monday but if it does work I'll consider it fixed and save some ££.

What I was really interested in was opinions as to what it could be as its a very unusual fault I've googled to death and not seen a similar fault so I don't want BG guy (or girl) being stumped and resorting to swapping out component after component and charging me for the lot of them or even worse telling me I need a new boiler.

for info, I had a bad experience with BG service engineer a few years ago, they came to service the boiler and I had my father round for the day. They told him it needed a power flush otherwise they might not cover a return visit (quote to follow which was ~£700) and tried convince my father of the fact by holding a magnet to one of the boilers incoming/outgoing cooper pipes and suggesting it was full of sludge. What I soon grasped when I got home and tested the same location myself with a magnet was he was telling porkies and the magnet must have had double-sided tape on it, there was no magnetic effect and when I drained the system just to be sure what came out looked like what comes out of a tap...crystal clear. I refilled with cleaner then a few days later drained again (still crystal clear) and refilled with inhibitor. Point of this story is a) I don't 100% trust all engineers as default (I know most are honest and genuine) and b) I don't like paying for things that aren't needed eg multiple part swap outs till its fixed. so just want if necessary and my new ignition PCB doesn't work to perhaps suggest something Monday to the engineer gleaned from the internet if he's stumped as I know he'll try thermistors first, then PCB and I'd have done both of those

 

[Moi]

I guess no one likes my BG £700 scam story

For the record and to complete this thread. today I received a second ignition module I ordered - same part number just not dipped like the first one. Fitted in 2mins going NO WHERE NEAR GAS components and I didn't bill myself [so all legal as not profit made] turned the boiler back and and bingo, its working perfectly again. Steady green light, burner fires up on CH & HW and constant but modulated flame.

First seller obviously sold me a like new dud, I'll be getting a refund for that.

Thanks for all your help

 

[ianmcd]

Glad you got the problem with your boiler sorted, the reason you didnt get answers is because you said you had changed the thermistors, in order to do that you opened the combustion chamber, whether you charge yourself or not you are not qualified to do that, I am not the CC Police , just telling you why no one got involved nothing else

 

[Moi]

I didn't have to remove the cover on the combustion chamber, only the main white metal cover at which point I could access the lower thermistor (this used a snap pin to hold it in place) and the upper one which is on a pipe external to the main chamber. Both hold water not gas (as I know you'll know

I understand your point though, anything gas related has to be treated with respect and there are some who might not know where to stop, perhaps I passed what some consider acceptable but I honestly believe myself competent in ruling in out certain non gas bearing parts....got it wrong with the thermistors perhaps but they were cheap, was right on the ignition board.

Co-incidently, I'm fairly sure the boiler started playing up when I think we had some sort of overnight power cut or surge, I recall my son wasn't too happy the TV HD recorder for some reason failed to record very early morning MotoGP the same day so likely we had a power issue and thats what damaged the PCB.