On Sun, 17 Oct 2004 23:07:00 +0100, "Ed Sirett"
wrote:

On Sun, 17 Oct 2004 12:18:53 +0100, Set Square wrote:

In an earlier contribution to this discussion,
Dave£ wrote:

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.

Anyone tell me what the problem is?

Many thanks,

Dave L


From what I've read about Combis, it sounds like a classic case of diverter
valve failure.

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.

Thanks to all for the help.

Dave L