Christian McArdle wrote:
I have a gravity hot water & central heating system with a rather
strange (from what I can see) setup. The hw cylinder has the
standard
thermostat attached to it which operates a 2way valve, when the
tank
reachs the set temperature.

All sounds good so far.

Unfortunately when the valve closes, this also causes the central
heating to stop. The ch pump is still spinning (if room thermo
wants heat) but it seems that no water is flowing round the
circuit as the rads go cold and the pipe leading to the pump
goes cold as well.

There clearly should be a system so that when the CH is calling for
heat,
the boiler should fire. Unfortunately, we need many more details to
make an
educated guess as to why it isn't.

See if you can answer the following:

1. Has the system ever worked? (i.e. could it be a
design/installation
fault, rather than a failed component).

2. What sort of zone valves do you have? You mention one for the hot
water.
Are there more like this one? How many pipes emerge from the valve
you have
located? Are there any markings on the valve?

3. Does the pump run for hot water as well as central heating, or is
it
purely for the CH?

4. What is the make and model of boiler?

Christian.