Heating comes on when control clock is "off"

[versatile75]

is there a frost stat fitted to the system? Roy

 

[abenn]

Not sure. Most engineers said "no", because it's completely indoors, but one engineer said "yes" and replaced temperature sensors on the feed and return pipes inside the boiler casing. But I'm not sure if those sensors are for frost protection or general management of the system -- maybe both.

Anyway, today another more-senior engineer came and, for the first time, he pulled a DVM out of his toolbox and started tracing circuits and signals between the boiler, controller/timer, and zone valves. He eventually concluded that the one-year-old controller/timer is faulty, since at the time of his visit it wasn't sending a signal to switch on the upstairs heating zone when the thermostat requested it. A new unit will be fitted tomorrow, so we shall see ....

 

[abenn]

... another engineer came with the new programmer and, on taking the old one off the wall, found a loose wire just lying against the terminals (not even in a terminal) on the backplate. Put it into a terminal, and installed the new programmer, though he admitted we probably didn't need a new one. Then upstairs zone valve wouldn't actuate, so he took it off its backplate and found another loose wire, which he then tightened. Still didn't work, so he took the programmer off and moved the once-loose wire to its correct terminal

Now all that's not working is the hot water! It worked when the engineer was here (of course), but the valve intermittently seems to jam in the open position without triggering the pump or boiler. So then water only heats up when one of the other zones is running. What's the betting it's another loose wire somewhere?

BG's diagnostics-by-replacing-components system doesn't seem to have worked in my case. I wonder how many of the valves, PCBs, sensors, and programmers they replaced (several of them twice) were really needed, if only they'd gone round and checked all connections first