netaheat electronic boiler problem

[kim.hayward]

My netaheat electronic boiler will switch on, piolot light, then full flame for a few seconds then switches off. Any dieas what may be wrong? It was really going well up until now.

thanks Kordi

[John Stumbles]

pump not running or other blockage in system? feed pipe from header tank to system blocked (scaled up)?

[Ed Sirett]

Does it do this repeatedly over and over again or just once in a while (with no flames at all in between) say every 20-60 minutes give or take ? Probably fires for about 60s initially.

1) If once in a while then probably there is no primary circulation (pump problem, blockage etc., lack of water! due to stuck float valve in loft)

Otherwise

2) Flame detection problem. The flames light but the electronics/ electrode are failing to register the flames so the control unit shuts down. Then (because it's a fairly simple control unit) starts over again. Problems include: crud on electrode, broken wire, electrode not in flames, faulty electronics). Note that the pilot flame is detected initially but the same electrode and circuit fail to detect/confirm the main event.

[geoff]

Additional info for Ed, John, etc ...

The netaheat pcb is a bit quirky in that the pilot valve falls back from pull in voltage to holding voltage via a relay

If there is a failure in this area, it could cause the problem

[Ed Sirett]

Thanks, I wasn't aware of that trick. A diagnostic for that would be that you'd here the pilot valve click off (due to the relay problem) then a moment later the main valve would close due to the flame sense failure.

Does the main valve also have this "feature" of diffeent pull-in and holding voltages?

[geoff]

No, just the pilot

It's weird - not seen it anywhere else

That's what the big green power resistor is for, it's the voltage dropper