Glow worm compact electronic boiler dreaded red light

Our Glow worm compact electronic boiler keeps cutting out with an increasing frequency. We had a similar problem a year ago and had it looked at by a Corgi/gas safe engineer who essentially repressurized the system. He commented that the floor was damp below the boiler and considered a leak, but at a follow-up visit (service) stated all was okay.

Over the last 2 weeks, the boiler has cut out approximately 11-12 times, usually in the morning. We have noticed that the water out of the hot water tap is excessively hot just before and after the boiler cuts out. The boiler makes a slightly unusaul whirring noise when the red light flicks on. Current pressure approx 0.7bar. Should I just re-pressurise or is there a more sinister problem? Many thanks.

It would sound that the DHW diapragm has stretched or there is carp behind it causing the boiler to carry on firing after the tap has closed.

It is the one on the right of the plate heat exchanger. Turn the power off to the boiler and remove the front cover to access. remove the microswitch and run a hot tap - pin moves out. Now turn the tap off, does the pin return quickly and fully?

http://www.glow-worm.co.uk/stepone/data/downloads_sd/4f/00/00/compact80e.pdf

Its unusual for a failed diaphragm to send a compact into lockout. Having said that, a failed diaphragm is the commonest fault on them and I regard them pretty well as a service item, so unless its had a HW diaphragm recently I'd change it anyway.

At 0.7 bar I'd expect a Compact to run, but those gauges are not all that accurate, so if it is in fact a real pressure of 0.5 or less, it might go to lockout. Also the boiler should be pressure set to bewteen 1 and 1.3 bar when cold and should not lose pressure. If you are having to re presssurise it more than three or four times a year max. then it suggests a leak, which ought to be investigated. Putting fresh water into a system on a regular basis maximises and encourages internal corrosion/sludge etc.

My best guess on this is that you have a scaled up/blocked DHW plate to Plate Heat exchanger which is putting the boiler into overheat and locking out as a result. If the system water really is filthy then a flush is required and it must be refilled with a quality corrosion inhibitor

I do not think this is a DIY job personally

Alfredo

Foxley20 said:

We have noticed that the water out of the hot water tap is excessively hot just before and after the boiler cuts out.

Click to expand...

Blocked plate would give poor DHW

Yes but with a blocked DHE Heat Ex its not uncomon to get a little burst of red hot before it all goes cold, so the DHW heat ex has to be checked out at the very least for blockage. Its sounds like an overheat lockout too which ties in with the boiler being unable to get rid of its heat into the DHW heat ex.

It may not be of course, but you can't ignore it as something to check.

Alfredo

the stuffing box where the pin comes out to make the dhw micro-switch are really common for leaking. they norm leak into the switch and create a false dhw demand causing the boiler to overheat.
just remove the switch and check if it is full of water

Many thanks Alfredo, Beerlover and gas_man_gaz. I think this is a job for the professional. Will track down a gas safe engineer this week. Any suggestions of one in the south london/surrey area would be much appreciated.