No hot water with combi-boiler

[Eric Sean]

Hi,

sorry to ask what seems to be a commonly asked question. I have an Alpha

240x combi-boiler. The other day, I noticed that I am no longer getting hot tap water from the system. The central heating system works fine, however - and if I turn the hot water tap on after the central heating has been on for a while, for a few seconds I get some hot water, but then it turns cold soon after. When I turn on the hot water tap, I no longer hear the boiler firing up like it used to.

Can anyone help with with a basic prognosis, or give me a clue how to find out more information on what is wrong with it, before I call a plumber and get fleeced? From reading google groups, it appears that it may be the diverter valve that has a problem.

If it's any use, the problem seemed to start the other day when my washing machine was on a cycle, and I simultaneously had a hot water tap running in the bathroom (sink... I was shaving...).

Hope someone can help.

Cheers.

[Christian McArdle]

As well as the diverter valve, it could be the flow switch that switches on the boiler (and controls the diverter valve) when hot water is demanded. As you have hot water for a brief time after the central heating, it suggests that when the boiler does fire, it does heat up the DHW heat exchanger. However, there doesn't seem to be substantial flow through the primary circuit side, as it doesn't stay hot.

Christian.

[IMM]

Not that quick though. It takes a time for the ground temperature to change enough to affect the mains water temp. Note that when the heat wave was on the mains water was still cold, as the hot air temperature above the ground did not heat the ground enough to affect the pipe 1 metre down.

[RichardS]

Good lord, never thought I'd see it.... due deference to the laws of physics from IMM... I _do_ need a holiday!

Yup, it's true. Don't have my old lecture notes to hand, but ISTR that at a certain depth you'll find a complete phase reversal, i.e. it reaches maximum temperature in the depths of winter, and minimum at height of summer.

Cheers Richard

-- Richard Sampson

email me at richard at olifant d-ot co do-t uk

[IMM]

You do need to look at your primary school physics book. At a certain depth the ground temperature lags 3-4 months behind the seasons. hence coldish in the summer and warmish in the winter. So the ground temp is about right to extract heat or coolth in summer and winter.

Read "The Whole House Book". Please read it 4 times.

[The Natural Philosopher]

IMM had to read it that often just to undesrtand all the big words.

[IMM]

Is that snotty uni wit?

[The Natural Philosopher]

I don't know. You are the snotty one.

[IMM]

Is this more snotty uni wit? Do you laugh at Last of The Summers Wine?

[Fishter]

Is this another snotty argument that we could all do without hearing?

[geoff]

In message , IMM writes

... ... ...

Ah - I knew he mush have read it somewhere

[The Natural Philosopher]

No, I drink it or more usually, cook with it.

[Paul Symons]

Finally got a gas engineer from a local Alpha registered maintenance company to fix it. It turned out that the diaphragm bit had split (well, had a tear in it). Therefore, the water pressure was never building up enough to fire the boiler. Haven't been invoiced yet, but I can't imagine it's a very expensive part, and only 1 hour of labour (although it only took 20 minutes to fix). I'm happy. Thanks for the helpful replies.

Paul