Hi hope someone can help, i have got a good grasp on the elec controls for my CH system but cant work out why i got approx 100v back feeding down to the room stat sw line. First fault occured was boiler constantly trying to re-ingite (mother board relay firing) i conducted full auxillary checks on timer, stats etc, then finally got gas safe enginner in and he along with tech support from wocester diagnosed main boiler pcb faulty. I have since changed board and fault cured, but am concerned that this backfed voltage now present at stat could have blown up pcb, any ideas?
Central heating controls
- Thread starter gsparks
- Start date
You can get back feed on a mid-position valve. It only occurs when the valve has been in the CH only position and CH is satisfied. It comes from either HW OFF or HW stat SAT and resistor R2. The resistor drops the voltage to 100V so it is below the voltage on the orange wire is insufficient to ignite the boiler by opening the gas valve or to run the pump.
It's a "feature/flaw" in the design of the mid-position valve.
These diagrams explain the workings and why it happens:
View media item 17313
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