Ravenheat CSI 85T failure to spark.

[Adrian C]

A neighbour has this combi boiler out of action with the overheat LED coming on solid after a few seconds, and no fan spinning.

I deduced fan failure and narrowed it down to a faulty relay on the main PCB. I've replaced that, and it's now got a running fan, pump, empty condensate trap - but no ignition, absolutely no attempt at sparks and no voltage at the gas valve.

Thinking something phutt has gone wrong with part of the PCB that drives the ignition voltage generator, but then again it could be some programmed line in the micro yelling 'If adrian is messing about with me, just be as safe as possible'.

These neighbours haven't washed themselves in hot water for three days and their dog looks a bit distressed....

I'm thinking I might soon be running in the direction of Geoff for a recon PCB but is there anything else I've missed?

[chudford]

Have you checked the air pressure switch?

[Adrian C]

Yes, but that was with me blowing through the tube. Probably the gust of the fan is insufficient to activate it? I'll recheck.

[geoff]

In message , Adrian C writes

If you have neither gas or spark, then it would point me in the direction of the air pressure switch not transferring (for whatever reason - e.g APS failure, blocked pipes or some other blockage) or hall effect sensor in the fan, depending on which it has, I can't remember

[Adrian C]

Thanks Geoff,

Yup, looks like the differential pressure sensor is kaput. Shorted it out it's connections after the fan came on, and the boiler fired up. This sensor is mounted near the top of the sealed plenum chamber, and the tiny vent hole for the switch is clear. We did a suck/blow test of the switch when we removed it, but human breath is not that well calibrated I suppose.

Probably have to do some more diagnostics after that to get the DHW supply working after we've fitted the above. Noted that even though the microswitch from the diverter valve works (and is switching 30V through the PCB), it doesn't do a DHW startup. I'll scratch my head on that next.

So so far I've got

1) a dead fan relay, presume burned contacts - replaced works 2) a duff pressure sensor, replaced will work 3) something else wrong with DHW, another sensor fail?

That's a combination of calamities, with no one event for blame. Is this

4yr old boiler crap or is it just me? Neighbour tells me it's their second.

[chudford]

My son has one of these and it is forever going wrong.

The DHW failure on his was the diaphram in the diverter valve which had perished.

You can get replacement diaphrams which are fairly easy to fit.

[chudford]

By the way the plastic replacement pressure switches sometimes don't work very well, I replaced his with a metal one I had and it now works perfectly (at the moment!!!)

[geoff]

Flow switch? Diverter valve microswitches not feeding back to the pcb - contacts or plunger operating the microswitches not lifting for whatever reason (split diaphragm ?) ?