David W.E. Roberts wrote:
Hi,

just had a wonderful week in a holiday cottage in Devon, with a slightly
nervous start after I tried to fill the bath :-)

Sequence of events; arrive at cottage and turn up wall mounted thermostat
(which is set to 'always on' and a low value as frost protection).
Radiators warm up and after a while all is toasty.
Hot water for washing dishes comes through fine.

I start to run a bath.
The water comes out piping hot but after a while I come back and check and
the water is running cold.
I turn the bath tap off, and seek out the boiler to investigate.

The combi boiler seems to be working, so I leave the front flap open so I
can see all the lights and stuff and turn on a hot tap. Water runs hot for a
bit, then runs cold.
Too much cold water flow?
However, the boiler is not running flat out but is clicking on and off.
The burner is off when the hot tap is on and running cold water out.
I notice after a while that the radiators are cooling down as well.
Panic slightly.
Go away for a restorative and a think.

After a while the radiators warm up again.
Further investigation reveals that once the radiators are warm then I can
run about 1/3 of a bath before the water runs cold.
Wait for 15-20 minutes and run some more hot water into the bath.
The water is hot enough that you eventually get an acceptable bath after
about an hour.

Now if I hadn't been watching the flame in the boiler, it would all have
seemed very simple.
Underpowered boiler can't heat radiators and bath water at the same time.
Running cold mains through the boiler cools the whole thing down resulting
in cold bath and cold radiators.

However I was watching the flame and it was off most of the time.
This is the bit I don't understand.
If there is cold water running through the boiler, surely the flame should
be on all the time?

Could some kind person suggest what the flock is going on?

Cheers
Dave R




Most combis devote all their power output to the hot water when its
demanded. I think we would need to know your make/model of boiler to
comment futher.