wickes/halstead HEAT 60 flame failure

[noflame]

Hello everyone, hope you can help. I have a Wickes Heat 60 boiler which once or twice a day suffers flame failure. Everything (fan,pump,etc) is running but the "flame failure" neon is on and its not burning.There is no particular logic as to when this occurs either. I have measured the thermistor resistasnce at about 8.36K and dropping with increase in temp- the fault finding chart says it should be at least 14K.
I am no boiler expert so this is as far as I want to go myself with the gas side of it although the electronics wont be such a problem if I know what to look for- does anyone have a clue whats happening here as I don't want to get ripped off so I would like to at least have some idea of wether I am being fed bull manure or not when I get someone in to look at it.
Thanks in anticipation.........

 

[noflame]

As a bit of further information, this only seems to happen when the boiler has been standing for some hours and is stone cold.
When it tries to start the sparking is very much louder than normal. I then reset it and everything returns to normal and it fires up.

 

[ChrisR]

Did you really mean
"I have measured the thermistor resistasnce at about 8.36K and dropping with increase in temp- the fault finding chart says it should be at least 14K.
"

If you're OK with a soldering iron check the connection on the pcb which goes to the gas valve - inspect it first for dark grey lines across the solder. ie a crack.

 

[noflame]

Thanks, I will have a look. Looking through this forum there seem to be lots of problems with boards on various makes of boiler; no-one would put up with this on a TV set; perhaps a PCB is not really suited to the boiler environment..............

 

[noflame]

Problem spotted!!!

I caught it in the act of not firing up;luckily the pcb is inside a clear case. for the benefit of anyone else with the same problem watch it in the dark.

At the bottom of the pcb where the spark igniter plugs in ther is a small air gap; when the boiler fires as it should a small spark jumps this gap; when it doesn't fire up a much larger spark arcs across the back of the board and misses the igniter terminal entirely, earthing through the board to god knows where. This is what causes the much louder sparking sound when it doesnt fire.

Now all I have to do is find a spare moment to get the board out and find a way to stop it happening!!!

 

[ChrisR]

Well done! You might find the "proper " connection is now through a broken solder joint. Call BG, they'll flog you a new pcb for £200 or so...

 

[noflame]

Finally found the time and the fault is now fixed!!!!
There were no dodgy joints on the board; it just appears to be a case of sloppy quality control and poor design; I encased the soldered connections of the HT part of the board in epoxy resin, thereby properly insulating it, and the boiler now fires up first time, every time.
The circuit is not particularly well designed; I know nothing of gas but electronics I do understand-I noted that there are very few fused circuits; the gas valve circuit doesn't appear to be protected at all-any short in the valve will fry the board!!!
I suspect if I had got in a Corgi man they wouldn't have been able to sort it and would have just replaced the PCB, and it wouldn't have been cheap.
Its the problem that now afflicts much of the independant motor trade; mechanical bits no problem; electronics a world of mystery with faults fixed by replacing bits until the problem goes away.