Interesting Boiler Problem

I have an oil boiler, HR Wallstar which stops when it is most needed. Typically it will fire up in the morning and heat up the house etc. Then with the Amber light still lit and demand from the thermostats it will simply stop. The thermostat on the boiler is not tripping out and the boiler stays off even when everything is well cold. The thermostat on the boiler is up high.
this only happens when it is really cold, suggesting that may be the boiler is doing a bit of overtime and something is cutting out. The 'lock out' relay is not operating so oil shortage is probably not the issue...?
When in this stopped state I power off the isolator and power it up again it will start the ignition cycle very briefly and then stop.
After an hour or two it comes back on and works OK for a while. Typically on warmer days it doesn't seem to go wrong. The boiler service man can't find a fault.
Any ideas??
Jay
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little drop of water trapped in the line that will settle at the lowest point, and if in an exposed part of the run may freeze on occasion causing starvation. Just a thought.
Dave
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of weeks ago and it's come back with the same problem.
The customer has tried putting it in the fridge and then installing it, then heating the module and then installing it. It seems that it won't work when very cold (which sort of defeats the object)
I'll be getting the freezer spray out tomorrow to investigate
--
geoff

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geoff wrote:

I had a very old boiler that used to do this. Would get worse and worse, maybe locking out as well.
It was always a carboned up nozzle and carbon on the pghotodetctor that detected the flame.
Its probably worth servicing both items anyway, but if it persists, its something in the control circuits as geoff says.
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writes

I have a theory ....
Maybe it's condensation.
I have liberally sprayed the pcbs with conformal coating and tomorrow I'll attack it with freezer spray again.
--
geoff

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