Glow Worm Compact 100 issue

Le_Kirk

I am hoping that someone has come across this one before - it has me stumped. Boiler (as title) has been in for 16 years and works, new pump (couple of years ago), new main gas valve earlier this year, new main control board also earlier this year - so you might say there's not much left!

Problem is that at about 3 or 4 in the morning the pump starts to run. I thought this was due to the return water thermistor going faulty but if that was the case surely it would happen at any time, not just in the early hours. Switching system off, waiting a few seconds and switching back on results in the pump stopping after a few seconds. I do have a spare thermistor and changed it but no difference.

Alex1983

Does the boiler fire up? The pump is integral on a compact isn’t it, does it do it every day? If it does I’d disconnect the switch live from the pcb and see if it does it then, you would of proved if it was the boiler or system then.

Le_Kirk

Alex, yes the boiler does fire up, works normally all day and evening, then shuts down for the night. As it should, the pump stops after the thermistor "sees" the temperature fall and nothing happens until 03.00 (or thereabouts) when JUST the pump runs.

If I disconnect the live from the pcb, the pump won't run as there is nothing else to give it power. What I want to know is what, on the pcb, is causing an output on the pump feed.

Alex1983

Has the pcb not got live neutral and earth and then a LS connection. The LS connection is the switch live from the system, this is what you need to disconnect temporarily. The pcb controls the pump. I don’t believe the boiler has a internal frost stat so the thermistor is unlikely to be the fault. I would imagine if the switch live is disconnected and it still does it then it will be the pcb. With the switch live disconnected if it doesn’t do it you have something on the system providing power to boiler when it shouldn’t be.

southcoastrgi

Alex1983

There you go it has a internal frost stat, wouldn’t change what I do with disconnecting the switch live, prove weather it’s a fault at the boiler or system.

If it is the boiler check the thermistor ohm readings are in tolerance and then you’d have to be looking at the PCB I would think. Don’t know what southcoast thinks?

Le_Kirk

Food for thought on those comments. There is, as far as I know, no internal frost stat. However there is an external frost stat (fitted when the boiler was installed) and controlled by a pipe stat strapped to the return pipework. This all functions correctly, although it has not been required for a number of years and temperatures have not been low enough - despite the boiler being in the loft. According to the manual for the Compact 100 (and it is not a 100E) on the electrical diagram, there is no frost stat. This has only started happening recently and it does seem temperature related as it only happens half-way through the night when of course it is colder and it only started happening after the new pcb was installed. Could the frost stat be on the pcb? It would be unlikely but not impossible. Is it possible the temperature is affecting something on the pcb and causing it to bend flex due to expansion contraction (clutching at straws here). Why, also does the pump stop if the power is removed and reinstated? Will check out the pcb.

Alex1983

If southcoast’s information above is correct then the PCB will have the frost stat built in and will work with the thermistor to determine if it is needed or not.

southcoastrgi

Le_Kirk wrote: »

According to the manual for the Compact 100 (and it is not a 100E) on the electrical diagram, there is no frost stat

Page 6.......

Le_Kirk

Aha, it's a case of can't see the wood for the stage 2 frost protection! Thanks for that. I was looking for an actual frost thermostat but I see now that system is using the return water temperature to determine that it is below 10 degrees C and start the pump. Three things are then weird: -

1. Why has it taken several years for this to work?
2. Why does the pump not stop when the water from the radiators (which will be at room temperature - say 17 - 19) and/or the hot water cylinder heating coil reaches the thermistor? I suppose if the three-port valve was last in heating mode, only water from the radiators will reach the thermistor but even so, it will be above 10 degrees!
3. Why does cycling the power cause the pump to stop?
Could it be a faulty pcb?

Alex1983

A faulty PCB will cause 1&2 it’s probably miss reading the thermistor and thinks it’s cold then it is, 3 will stop it because the PCB is faulty and it’s resetting its self.

I would definitely disconnect the switch live from the boiler first, this will rule out any issues from the system it’s self before you spend any money on a PCB.