Should my radiators come on when the hot water comes on - even though the heating is set to "off" on the programmer, and it's so hot in the house that turning the stat up to maximum (30) does not cause it to "click" on?
No it should not. You have a wiring error or a fault with the valve. Call the installer back if it is a new system.
You've got a fault. Could be a sticking valve or a design/installation problem causing thermo circulation. If the latter you may need to add a one way valve.
It's 9 years old (built with the house). The pump was replaced recently but I visually observed the whole process and he simply did remove the old pump and refit the new one.
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There are various tap-like valves in the airing cupboard where the yellow cylindrical tank is. Could one of these be open when it should be shut or vice-versa?
The motorised valve near the pump seems to be sound, as I can hear it moving and water starting and stopping when it operates.
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Sorry I have come late to this thread and most has already expired so what I say below may already have been said before.
Are you sure that the absence of 'click' with the thermostat is it not turning on? Given the symptoms it seems more likely that the thermostat is not turning off. This is easily checked by disconnecting the thermostat (after isolating the supply).
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No, it clicks fine when the temperature of the room it is in is lower. On this particular day it was very hot, and I wanted some hot water for a shower, washing up etc. We had both the hot water and the heating set to OFF on the programmer as it had been a prolonged hot spell. I pressed the +1 hour button on the hot water side of the programmer and within about 10-15 minutes the radiators were on full blast, even though we had turned the stat down to 10.
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As I missed the earlier part of the thread I may be covering old ground but if the boiler is not responding to the thermostat something must be shorting it out. I don't know whether you have 2 port or 3 port valve control but I would have thought sticking valves and/or valve microswitches need investigating next.
Sorry but I will be off-line for the next few days so won't be able to take this conversation any further.
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Cheers for the input. I've booked a boiler service and motorised valve inspection for the next few days. Get it sorted once and for all.
I had a similar problem once. The wife got the data sheets from the manufacturers on the various valves and controls in the cupboard. Turned out we had a 3 position valve and a controller for 2 position valves. This meant that we either had "both" or CH only. The water would get very hot!
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