Hi,
Our combi boiler fires up when we put the hot tap on but after about 30
seconds it then stops again. After another 30 seconds it repeats the
process. Unfortunately this means we are unable to use the shower.

A British Gas engineer came round and, just by switching the hot tap
on, told us that the problem is not the boiler but the mains pressure
into the house and requested to call the water board.

They stated that if the neighbours are unaffected this would be
unlikely (which they are not). Also, the radiators still heat okay
(although they do not require the boiler to be constantly on).

Anyone have any ideas? I don't want to resort to digging up my drive
unless all other avenues have been explored.

Thanks
Neil

wrote:
Hi,
Our combi boiler fires up when we put the hot tap on but after about 30
seconds it then stops again. After another 30 seconds it repeats the
process. Unfortunately this means we are unable to use the shower.

What boiler is it?

The symptoms sound like a potential dodgy diverter valve (e.g. perished
diapgragm).

Mathew

It's a Potterton - around 5-6 years old.

Although the radiators are hot, the boiler still emits a similar
pattern when heating just the central heating, i.e. on for a short
period, off for a short period. I may be wrong, but I think the boiler
used to fire for much longer when heating the radiators before the
flame going out.

Would that still point it to the diverter valve?

One other thing. The cold water pressure from my taps is very high, the
hot water tap not so high.

In message . com,
writes
Hi,
Our combi boiler fires up when we put the hot tap on but after about 30
seconds it then stops again. After another 30 seconds it repeats the
process. Unfortunately this means we are unable to use the shower.

A British Gas engineer came round and, just by switching the hot tap
on, told us that the problem is not the boiler but the mains pressure
into the house and requested to call the water board.


This sounds like ********, (not a surprise with some BG engineers). I
have loads of combis, and almost the merest trickle from the hot tap
makes them fire up and stay on. In fact... to get the water hot, the
flow has to be fairly low. I use narrow bore shower heads to get a
reasonable shower "pressure".

They stated that if the neighbours are unaffected this would be
unlikely (which they are not). Also, the radiators still heat okay
(although they do not require the boiler to be constantly on).

Anyone have any ideas? I don't want to resort to digging up my drive
unless all other avenues have been explored.


Sounds like the boiler may be cycling too fast, and I would guess that
there is something in it which controls this.

--
Richard Faulkner

In oups.com,
scribed:
One other thing. The cold water pressure from my taps is very high, the
hot water tap not so high.

That sounds pretty normal to me and certainly doesn't suggest an incoming
cold water main pressure problem!

I tend to agree with Ed and point the finger towards the secondary Heat
Exchanger which I too had to replace just recently under similar symptoms to
yours. I had to buy a kit which included pipes, so it ended up costing me
just a shade under £100 inc VAT as a DIY fit. However, if you can just get
hold of just the exchanger itself, then it should be somewhat cheaper than
that. Also, don't forget to put some sludge removing chemical such as
Sentinel X400 Desludger (around £15 inc VAT per litre from a good plumbers
merchant) into the system to flush the gunge out, or you will only end up
blocking up the new exchanger again in short measure.

Nigel

Ed Sirett wrote:

The prime suspect is a scaled up secondary heat exchanger that won't allow
enough heat to go from the boiler into the HW.

If the model is a Puma then the CH delay is normal on-off 30seconds - on.
Longer than that it'll be the wax pellet actuator.
However it should not fire up and down repeatedly until the radiators are
hot.

The second British Gas engineer stated my water pressure was fine and
that the heat exchanger would need replacing due to limescale build up.


Before I get the quote, can anyone provide any insight as to what a
reasonable quote would be for parts and labour? Previous quotes from
British Gas have been halved by me obtaining the parts myself and
getting a local plumber/electrician to fit.