Intermittent hot water from combi boiler

Fixitrite · 8 Jan 2011

Hi
Just installed a thermostatic shower and noticed it runs hot for maybe 30 secs then goes cool for maybe 10 secs , then hot for 30 secs and continues on this cycle.
I hadn't noticed this before and thought the new shower was at fault but when running the kitchen hot tap the same cycle happens , boiler cuts out after 30 secs or so then re fires.
The boiler runs constantly when the heating fires in the morning but hot and cold water still occurs.
It's an Ariston Genus boiler about 12 years old.
Any ideas as to possible fault ?

Thanks.

petit_pablo · 8 Jan 2011

Most likely fault will be that the hot water plate heat exchanger is blocked.

mysteryman · 8 Jan 2011

Not just the heat exchanger, but all of the primary side of the boiler, usually by debris from the heating system.

Fixitrite · 8 Jan 2011

Thanks guys
Is the fix relatively straightforward or am I looking at big cost and maybe cheaper to replace the boiler ?

bengasman · 8 Jan 2011

The fact that your system is full of shyte will not be solved by replacing the boiler; the best solution is a good powerflush.

Fixitrite · 10 Jan 2011

Been thinking about the sludge build up and can't understand why the boiler cuts out when DHW is requested .
If I turn hot tap on there must be a valve or summat that allows the water to be heated, flow through the boiler must be sensed by a switch which operates a valve or similar. If the valve or switch was defective I'm thinking this could be the cause ??
I seem to recall that some valves are operated by a rubber diaphragm.
Are the switch or valve easy to check ?

Agile · 10 Jan 2011

There are many possible problems with your boiler and dirt is only one of them,

As gas settings are important you really need a competent engineer to properly check it and fix whatever it requires which may well be a combination of problems.

I have this feeling that you have never had it serviced!

Tony

systematic · 10 Jan 2011

Don't listen to Tony, he hasn't got a clue and will try and suggest more work than what is required at rogue trader rates.

As everyone has said, a Power Flush will most likely resolve the fluctuation in hot water.

On a side note, Tony has confirmed (on a separate thread) that he is a great fan of western mvoes, which to me is a red herring that he is a part-time cowboy.

Fixitrite · 10 Jan 2011

You are correct Tony - my boiler is operated on a reactive maintenance schedule !!
I do like to fix things but as you can tell from my questions I know very little about how a boiler works. I like to understand the fault and fix of thoings, and I'm struggling to understand the sludge bit.
I think I'll call the local heating eng out for a look at it, may even get it serviced too

Liked your comments Systematic

bengasman · 10 Jan 2011

Fixitrite said:
...Liked your comments Systematic

Be aware that systematic is a troll who has been banned repeatedly. He is not a pro, not a plumber and certainly not a heating engineer.

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Intermittent hot water from combi boiler

mysteryman

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