Set Square wrote:

In an earlier contribution to this discussion,
Jon Telfer wrote:

Hi,
I've just tried to turn on the central heating after it being off
all summer and there was a flash/bang/release of magic smoke.
I've not made any changes to the system since it was last working
OK. Any ideas/usual culprits? It was serving the hot water OK.
It's a horstmann controller and it's not a combi boiler system if
that's any help.

TIA + not looking forwards to tomorrow's shower,

Jon

We need a few more details about your system - gravity hot water and
pumped CH, or fully pumped? If fully pumped, how many - and what type - of
motorised valve do you have? [Likely either one 3-port valve (Y-Plan) or
two 2-port valves (S-Plan) - see
http://content.honeywell.com/uk/homes/systems.htm]

Seemingly, something which hasn't been used for a while has developed a
fault in the meantime. If it's a gravity hot water system, I would check
the pump. Otherwise, look at the valve(s).

Going from the last bit first - I have a single three port valve and a
single pump (Y plan I reckon).