A couple of times recently, the hot taps have been running cold, and the combi boiler doesn't fire up when a hot tap is turned on in the house.
I've also noticed a lot of air pockets blasting and sputtering from the hot taps when thy are first turned on. The unheated water from the the taps seems to be at a pressure high enough that would normally cause the boiler to fire up - but the water is coming out ice cold.
The central heating is working fine.
The boiler is a Britony Combi 80 made by Chaffoteaux et Maury.
For sure this is the HW flow sensor. I'm 99% sure this is implemented using a differential pressure diaphragm on this model. The diaphragm has split or the pin it move has jammed. Just possibly the microswitch it turns on has completely failed.
Thanks for that. That item was high on my list of suspects. This boiler doesn't seem to have a diaphragm such as you mentioned, but I have found the switch which I think you are talking about. I took it out of its hosing this morning to look at it. after removing the spring clip, I pulled it out an some hot water sprayed out for a moment. Looking at the switch, I see a brass plunger, about 3 or 4mm diameter. one the exposed part of the wsitch are two eires going to the control box. Is that the switch you are referring to?
Is there a way to test it - like with a volt meter perhaps? And if it proves defunct, is there a way to fix it - like cleaning some contacts inside, perhaps? I was going to replace the whole item today just in case it's faulty - but all the plumber merchants are closed, and tomorrow I'm supposed to be going away.
For all I know, you could be right. I'm just wondering though, that it might be that the pressure at the taps isn't enough to trigger the diverter valve or switch the pressure switch. I'm thinking of taking the secondary heat exchanger out to give it a descale. The flow is definitely impeded a bit.
Can I take the secondary heat exchanger out without draining the system? I tried isolating the boiler, but as soon as I started unscrewing the secontary heat exchanger, water started spraying out at fairly high pressure, so I tughtened it up again, fast!
I'm still wondering what might be causing all the air in the DHW pipes, which splutters out at the hot taps. Surely that must be a strong indication of something or other, yes?
Or - I think you might agree - it could just be that the water pressure between the Secondary heat exchanger and the hot taps isn't quite enough to trigger the diverter, yes?
I just increased the mains flow to the boiler, up to maximum (the fill mains pressure), and found that I then got hot water from the taps. The pressure at the taps was hardly noticeably different, but it might have been just enough of a difference to switch the pressure switch. Dos this sound feasable?
Don't agree the symptom the OP reports is that the boiler does not fire up when a HW tap is turned on. It might be that turning the water main on a bit more has temporarily cured the problem until the split in the diapragm gets bigger. If this model does not have a diaphragm I appologize but I think it does use this method for DHW flow detection.
A quick test of the microswitch is to activate it. Don't do it for too long or the boiler will over heat!
The manual for the latest model (Brittony SE) is on their web page. I doubt it is very different from what you have. The shape and size of the DHW sensor shows it to be a diaphragm diffential pressure sensor which directly operates a microswitch and the 3 way (diverter) valve.
Ed, Thanks for the input. You are right, and you are wrong. ;-) It turns out that this boiler doesn't have a diaphragm, but it does have a pressure sensor switch. It seems to be working OK, though the sealing "O" ring under the screw-on cap was badly persished (I'm amazed it was still making a sal) so I replaced it..
The technical help guy at the boiler's UK HQ, said that the diverter valve wouldn't be a problem (I' don't know why he was so certain, but I took his word for it. He said something about it being "underwater" and that they never go wrong!).
What I ended up doing was replacing the secondary heat exchanger. When I took it out I found that the DHW side was caked heavily with limescale. I tried to descale it with some acid but didn't have much success, so I decided to shop around for a replacement. I got one locally for about £100. A lot of money, but it was a new-improved version with bigger flow capacity, so I thought "What the heck." It was probably worth paying the £100 just for the better flow rate and the fact that it consequently won't get blocked so soon.
All seems to be working fine now. However I still haven't solved an issue with the pressure relief valve. I will post a new thread on that.
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