I've got a fairly new combi boiler and about a month ago the shower
started playing up... after about a minute of washing the water
temperature goes freezing cold for about 15 seconds, and then it's back
to normal before it does it again in another minute or so's time

At the moment it's fine cos of the hot weather, but Im not going to
enjoy this during winter!

I've tried resetting the boiler, but that was to no avail.

Any ideas?

wrote:
I've got a fairly new combi boiler and about a month ago the shower
started playing up... after about a minute of washing the water
temperature goes freezing cold for about 15 seconds, and then it's back
to normal before it does it again in another minute or so's time

At the moment it's fine cos of the hot weather, but Im not going to
enjoy this during winter!

I've tried resetting the boiler, but that was to no avail.

Any ideas?

Yes. You have long pipe runs and the COLD run is HOT because its in a
loft or somewhere..

That coupled with a low acting thermostatic shower mixer, will do
exactly what you are seeing. If the cold is actually hot enough, there
will be no demand on the combi and it it will NOT come on till the
shower 'runs cold' and even then, it has to shunt all the not very hot
water out of the pipework to get to the shower.

In winter the thing will simply run COLD until the combi water arrives.

ah ok, that makes sense

is there anything i can do to stop it?

And why didnt it do this last summer?

wrote:
I've got a fairly new combi boiler and about a month ago the shower
started playing up... after about a minute of washing the water
temperature goes freezing cold for about 15 seconds, and then it's back
to normal before it does it again in another minute or so's time

At the moment it's fine cos of the hot weather, but Im not going to
enjoy this during winter!

I've tried resetting the boiler, but that was to no avail.

Any ideas?

I have a similar problem with my combi. I've been told that it's due to
the secondary heat exchanger being clogged up, either with scale on the
DHW side, or with sludge/crap on the heating circuit side. The
consequence of this is that heat is not transferred efficiently to the
water flowing through the heat exchanger, the water in the heating
circuit overheats and the boiler cuts out momentarily until everything
cools down. The effect for the person in the shower is that the water
runs cold for about five seconds in every sixty. As you say, it's
actually quite pleasant at this time of year, but something needs to be
done before November comes round.

Apparently it's not that hard to solve. You need to remove the
secondary heat exchanger and soak it in the right stuff (Fernox DS3 I
believe) to clean it up. If you can pump DS3 through it so much the
better. There are some old threads on this which you can find via
Google Groups.

If the problem is sludge and oxide in the heating circuit (rather than
scale on the DHW side) that's symptomatic of general malaise in your
system and you should chemically clean the whole system, flush it
through and make sure it has adequate inhibitor in it. It may be that
the original installer did not put inhibitor in. Apparently some
heating engineers believe that it's not necessary in a sealed system
because there is no way air can enter the system. In my limited
experience this is rubbish which has more to do with saving them a few
quid for the cost of inhibitor.

Anyway, all this advice is hypothetical at the moment. I still haven't
got round to sorting mine out yet.