Hello Attended a property where a local boiler care company have attended a fault with the heating and have replaced the stat and then traced a fault on the programmer (Drayton Tempus 2). However the engineer refused to change the programmer as in his words 'there is a wiring fault, voltage present on neutral when boiler is isolated' He has 'bypassed' the timer so the heating is constantly on. Upon testing this I found that when the boiler is isolated there is no voltage on any of the wires at the programmer. When the boiler is turned on there is a backfeed of approx 20v from the live switch wire to the boiler. I assume this is just leakage from the PCB/components within the boiler and is unlikely to have caused the demise of the programmer. Shorting the live feed to the programmer with this live switch wire fires the boiler up as expected so do you think the fault is simply a dodgy switch within the programmer itself?
The programmer just has a relay output. You're unlikely to have a 20V back feed from the relay even with sticking contacts. What equipment did the boiler care company use to measure the voltage? To isolate the problem, disconnect the switch-live wire from the boiler terminal block and measure the voltage at the switch live terminal. If you can't do this as you have to remove the boiler cover and aren't Gas Safe registered, then isolate the wire from the programmer and measure the voltage on the switch-live wire from there.
This was already done with the programmer isolated, I don't think I explained very well. The voltage was measured on the switched live wire from the programmer (with the face removed) to the stat.
Presumably the setup looks like this: Does the thermostat have an anticipator resistor? If so, if a voltage is present on the boiler switched-live terminal, a small proportion of that voltage may be measured on the neutral terminal. 20V on the relay contacts will not damage the programmer.
Forums
Facebook
Twitter
You Tube
Instagram
Shop