Glowworm compact E heating ok but no hot water

[littlejohn]

My daughter bought a house 3 months ago and had the boiler serviced (a GW Compact E, 75 or 80 I think as it is only 1 bed terrace). All was fine until last week when, in the winter mode, the CH works ok but there is no DHWater. If she switches to the summer hot water only mode, then the DHWater works ok.

I am visiting next week and would be able to change simple things like microswitches and diaphragms but would like an idea of which parts to have available. I have the manual. Any advice gratefully received.

 

[Gasguru]

What Compact is it? - there are several versions, the pilot versions are entirely different than the electronic ignition version.

 

[littlejohn]

Hi,
It is a Compact E for electronic, either a 75 or 80 I believe as I haven't had the cover off yet. Definitely no pilot light.
Thanks

 

[Gasguru]

From what you describe that's a bizare fault I can only think it may be pcb related...are you sure the description is correct?.

If it is indeed board related on this boiler you must not just change the board...there are several adjustments required requiring a corgi since it involves measurements on the gas valve.

 

[littlejohn]

Thanks, gasguru, for the reminder about the PCB not being a DIY job. I was only thinking of changing the diaphragms/microswitches at the most if these are leaking, as described in other posts. I shall check the description of the fault again with my daughter tomorrow more carefully.

She originally called to say that she couldn't get hot water at the bath or sink but the heating was working ok. I told her to switch it to summer mode and try again which she did. She was then able to get hot water at the sink and,after that, at the bath tap. She has been doing that for a week. I'll repost tomorrow when I have confirmed the details.

 

[littlejohn]

Hi, Gasguru,

Well I have been checking the fault again, albeit from 700 miles away, by telephone. The situation is not as clearcut as I first said. My daughter still says that she can get water to bath in on the summer setting virtually all the time, but this is not roasting hot and doesn't need to have cold water added.

However, this evening whilst she was on the phone, she turned the boiler onto the winter setting and then opened the kitchen tap fully. The DHW demand light, which she says always has a slight glow (may be significant), lit up even more. The burner light was on but the water did not get more than luke warm. So I told her to switch to the summer setting and try again. We were both surprised that the water still did not get hot, even trying it several times. So DHW appears not to be ok on the summer setting, at least not consistently.

It is perhaps more likely that this is a case of CH ok but DHW not ok most of the time. I wonder if you have more thoughts on this and what bits I may usefully arrange to be there next week?

Thanks for any of your consideration. I have found it very informative to follow the threads of combi posts.

 

[Gasguru]

Opening the taps fully (especially bath taps) will often result in the water being lukewarm despite the boiler firing up. The boiler can only heat the water to the required temperature at a specific flowrate. If the water runs through the boiler too fast it can't heat it so much . A Compact 80 will heat a bucket of water a minute to bath temperature. Remember at this time of year the incoming water is much colder so the taps have to be turned down more than in the summer.

I have seen the dimly glowing DHW demand light despite there being no demand, it may be the result of a water logged DHW flowswitch (can't remember precisely).

Since the boiler appears to fire up with fully open taps (despite the water being luke warm as described above) I would take the following.

DHW flowswitch (existing one could be waterlogged)
DHW diaphragm (existing one possibly perforated)
DHW diapgragm brass cover and gland assembly (often the gland seal fails).

This lot may cost around £30 but it is a weak point on this model and often require changing every couple of years (on SE London water that is).

You will need a Torx screwdriver (or bits) for the DHW cover assembly screws.

Of course it could be pcb related but this would be a reasonable starting point given the ambiguious description.

 

[littlejohn]

Thanks, Gasguru, for the pic and advice. I shall order bits as described and will post again once I have seen the insides, approx 8 days hence.

 

[littlejohn]

Hi, Gasguru, Oh Wise One.
You were absolutely right, but not in the way I expected. On arrival I could see the DHW demand light glowing dimly with taps closed. I took off the case front and dropped the control panel, expecting to see leakage. However there was none and the boiler looked absolutely pristine. I tested the DHW microswitch with a meter as per the manual and it was functioning correctly, tap open and closed.
So I then went back to your first point and ran the bath tap only slightly open, waited for what seemed an age with luke-warm water and then, hey presto, it worked perfectly. I then explained all this to an embarrassed daughter! We now have a collection of spares for the next time which is no bad thing. At least she didn't call out Glowworm for a non-existent fault @£210.
Once again, thanks for your help.
Regards, John