:-( Central heating issue

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Morning All!

Cold start in East Anglia this morning.. woke up to the central heating not working. It's been a bit flaky this last couple of weeks.

Boiler is firing and hot (oil boiler. Not combi), central heating pump is spinning away (brand new), water pressure is showing 2bar, the feed pipe is lovely and hot coming out of the boiler but the return to the boiler is stone cold.

Worth mentioning that there are three things in the cupboard upstairs (see pic):

  1. Sunvic 2 port spring return, motorised actuator (the white block on the picture)
  2. Honeywell valve of some sort (the corroded/dirty silver looking thing at the base of the tank)
  3. Auto-bleeder (black cylindrical thing - Unrelated to this problem but shouldn't this be higher than the tank?)

Went up to the airing cupboard to see if the feed pipe to the actuator was hot, it's not. The motor head , however, is hot. Removed the motor head from the brass valve and manually 'actuated' the valve (it was already open, actuated it through closed-open-closed-open), waited for a bit, but the pipes on the actuator still didn't get hot (boiler still on and central heating pump running at this point). Switched the mains power off to the boiler and the motorised actuator head returns to it's normal position (closed) and is no longer getting hot. Feed pipe to the hot water tank isn't hot either.

Switched the system back on, set to hot water heating and the feed pipe to the water tank is getting hot but the pipe to the C/H actuator is still not getting hot....switch hot water off and by the time I get upstairs the feed pipe to the actuator is hot...!!!!!

Anyone have any ideas what this is??

Cheers!

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Pump spinning does not mean it is moving the water
If there is no water or system air locked, water might not circulate
Lot of variables which will need a heating engineer to visit and sort
 
By its location, the Honeywell valve can be identified as being responsible for controlling the flow of water from the boiler to heat the hot water cylinder. This then leaves the Sunvic valve responsible for the central heating. When either of the valves are opened by the controls (programmer / thermostats) they have an internal microswitch that will switch on the boiler and pump.

It is possible that the central heating valve is not opening, but it is fairly easy to check. There will be a manual lever protruding from the base of the actuator. With the heating set to be 'on' and the room thermostat (if present) set to maximum, slide the lever to the manual position. If it feels loose and floppy, as if it is not connected to anything, the valve is open, if there is some resistance, and a whirring noise can be heard when it is released, the valve is not opening, and is most likely faulty. But be careful, although much less common, a faulty room thermostat or programmer could also cause the same symptoms. So electrical testing of the components would be required.

The odd bit about your post is:
Boiler is firing and hot (oil boiler. Not combi), central heating pump is spinning away (brand new), water pressure is showing 2bar, the feed pipe is lovely and hot coming out of the boiler but the return to the boiler is stone cold.

This is odd because one or both of the valves would need to be fully open for the boiler to run so there should be an 'open circuit' (ie around the hot water cylinder, or radiators) between the flow and return meaning the boiler return will get hot. Also you don't mention the how water cylinder, it that working OK, if so the return pipe to the boiler must be getting hot when that is working.

Also you say the pump is "brand new" it may be possible that an airlock has been introduced when the pump was changed, especially if the local isolation valves didn't work and the system had to be drained.
 

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