Heating conundrum

[Turpstornados]

I have an unvented central heating system, there are a couple of problems.

The PRV on the cold water inlet is slightly leaking, the water leaking is cold.

The boiler is under warranty and we have an engineer scheduled to arrive next Weds to resolve the cold PRV water leak.

The system has 2 x 2port motorised valves, I have checked both valves and the mechanical valves open and close and both motors are working when the respective thermostat closes them.

The pressure gauge by the water tank is reading 1.5 bar and the boiler read out is 1.7 bar, the radiators have all been bled in the last 24 hours. I have already replaced the hot water valve motor head as this appeared to be the initial issue.

However, when the hot water is heating up the central heating is on, although the radiators aren’t particularly warm.

When the hot water gets to the set tank thermostat temperature the hot water 2 port valve closes and the boiler stops, even if the heating thermostat is still calling for water and the heating valve is still open.

I have tested it by disconnecting the motor head from the hot water valve and physically closed the valve, in the above scenario the boiler remains on and the radiators warm until the room thermostat reaches temp and closes the heating valve.

Is the hot water/heating on off issue likely to be resolved by the PRV issue being fixed? If not any ideas as to what the issue is, the boiler warranty repair won’t cover anything that isn’t directly involved with the boiler. But we don’t want to get an independent engineer out and find the “free” warranty repair would have solved it.



Any ideas or thoughts greatly appreciated

 

[oldbuffer]

1. I would very much doubt that fixing the PRV will have anything to do with problem of the heating not working once the hot water valve switches the boiler off.
2. I would suspect the central heating motorised valve. These valves have a micro switch in the, and work as follows:
2.1 The valve is normally closed by spring pressure.
2.2 If the central heating thermostat requires heat, it applies a voltage (usually mains) to the CH motorised valve.
2.3 The motor in the valve operate and turns a toothed sector segment.
2.4 The segment opens the valve by rotating its spindle.
2.5 When the valve is fully open, the segment turns the microswitch to "on"
2.6 The microswitch applies a voltage (usually mains) to the boiler's switched live terminal, causing the boiler to fire.
3. It is possible for the microswitch to fail, or for the segment to fail to reach far enough to close it. In such case the valve is open (and thus will take hot water from the hot water circuit if that happens to be on), but the boiler has not been told to fire.
4. Depending on the make, operating the manual valve opening on the motorised valve will not move the segment far enough to close the microswitch.
5. Depending how experienced you are, it is possible to test what is happening with a multi-meter, but there are mains voltages involved so it can be lethal!
6. The easiest approach is to remove the head and replace it. While removed, check the spindle can be moved easily (they usually don't rotate more than around 30 degrees, but varies by make). If it can't be moved by hand, or with a little effort with pliers, replace the entire valve.

 

[Turpstornados]

Thanks, will replace the CH valve motor and see if that sorts it.

 

[Turpstornados]

Hi, thank you, changed the heating valve motor and all fixed!