"Adam" wrote in message
om...
(Adam) wrote in message
. com...
Hi All,

snip

The knocking occurred at least twice last night - once around 1130,
once around 0230. The hot water was turned off at the wall thermostat
for the boiler.

There is, however, a switch in the hall near the boiler that says 'hot
water' or similar with a red light embedded below the switch itself.
Switching this off caused the knocking to tail away. Switching it
back on caused the knocking to return after a few minutes. Now, that
sounds like an electric element heating water to a boil to me...

Have we got electrically heated water in addition to the gas boiler?

Yes, or even only electrical.

When we first moved in and switched the water on (at the boiler
thermostat), we were expecting nearly instantaneous water because we
believed we had a combi, but there was no hot water until we switched
this 'hot water' circuit on (and then we had to wait a half hour or
so). Has this been installed in the past because someone couldn't get
the boiler to heat water?

It would have been installed anyway as part of the original installation, if
nothing else as a backup. Accepting that...

If you didn't get any hot water until you turned on the electric heater,
possibly, or maybe the boiler was never designed/installed to.

Most importantly, can I find out what in
installed in my house without paying a fortune to get a plumber in to
suck his teeth and tell me I need to spend a fortune on replacing it
all?

Find out exactly what stuff is there and post again here. Follow pipes,
especially around the boiler and the tank. Find out *exactly* how many pipes
enter the hot water tank and where. If, for example, there is one pipe out
the top and one pipe in the bottom, then the only water heating you have is
electric.

As you are getting boiling, the the thermostat for the tank may be faulty.
This is a relatively simple DIY task to change but involves electrical
connections. If you feel you are not competent, get someone who is. It will
be found under a cylindrical metal cap on the cylinder somewhere (isolate
before taking the cap off). The thermostat will slide out separately and cna
be replaced (with one of the same length). There is clearly nothing wrong
with the element itself!

So, either:

1. Your only water heating is electrical by design - expensive to run,
expensive to change (but, bar the thermostat possibly, it is working!)

2. The water heating part of the heating circuit driven by the boiler (if it
exists) is not operational. Shouldn't be too expensive to fix.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)