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
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.
Anyone tell me what the problem is?
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
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.
On Sun, 17 Oct 2004 12:18:53 +0100, "Set Square"
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
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
Thanks to all for the help.