Heating by itself not working

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Hi all,


Tried turning the heating on today, with thermostat set high.

Boiler doesn't fire up, neither does the pump.

If I select hot water and heating, the boiler fires up and the rads start getting warm.

In the past, I have fixed similar problems by removing the Drayton 3 port motorized valve, and with a spanner moved the spindle to free it up a bit.

Doesn't seem to be this, this time around. If I select the 3 different modes on programmer, I can see the indicator on the motorized valve move between W-M-H okay.

Any ideas what it may be?

Cheers.
 
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It may be micro switches inside the motorised valve, some times latching the bleed lever on motorised valve will give a temp fix to keep it running. But only real fix is new head or valve.
 
Is the bleed lever the little black plastic spring one that sometimes pops out? Currently in the heating only position it is in, and won't budge. I'll select mid or hot water so it pops out, then manually move it back to heating to see what that does.

When I select hot water and heating together, the boiler fires up, and rads start getting warm. However the pump in airing cupboard seems a lot quieter than I seem to remember. To the point I'm not sure if it is running or not. There does feel like some rumbling in the pipework.

Would a malfunctioning pump cause the boiler not to fire?

IMG-20210429-170554.jpg


IMG-20210429-170548.jpg
 
Would a malfunctioning pump cause the boiler not to fire?

No, it would cause the boiler to cycle on and off, plus possibly trip on overheat because it cannot get rid of it's heat to the water.

The cause of your issue would seem to be the 3-port valve and it's actuator. If you can remove the actuator, then you should be able to turn the valve spindle with reasonable ease, almost with your bare fingers. If you can, then you can get away with just fitting a replacement actuator (the motorized head of the valve).

Replacing just the head is a quick job, versus the much longer job of replacing the entire valve complete.
 
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No, as @ericmark says, there is a microswich that switches on the boiler when the valve winds fully across to the heating only position that is the usual cause of this problem. The pump appears to be working as you said the radiators heat up when hot water is selected.

I think 'bleed switch' is a typo and he meant to write 'black switch'
 
I could take a gamble and get a new motorized head. Before I do however, would there be any way to confirm it by fudging the microswitch somehow?

If the M and HW positions fire up the boiler, and CH doesn't, this would seem to indicate 2 out of 3 microswitches are working. I thought maybe it was the valve spindle being to tough to turn, but I freed up with spanner. Plus even tried with the motorized valve not connected to the spindle. Still didn't engage boiler. I did notice the motorized valve felt quite warm.

Sorry rambling a bit
 
If the M and HW positions fire up the boiler, and CH doesn't, this would seem to indicate 2 out of 3 microswitches are working. I thought maybe it was the valve spindle being to tough to turn, but I freed up with spanner. Plus even tried with the motorized valve not connected to the spindle. Still didn't engage boiler. I did notice the motorized valve felt quite warm.

Either that or the actuator is failing to move to the heating position. 'Warm', is the heat from the motor - in any position other than off, the motor is powered so it gets warm. The motor is powered against a strong spring.

Its the (essential) sheer strength of these springs which causes so much wear on these units and unreliability.

I could take a gamble and get a new motorized head. Before I do however, would there be any way to confirm it by fudging the microswitch somehow?

I could and I perhaps would, but I would never suggest that anyone else tried that. You could maybe remove the plastic cover with the power off and take a look inside. The microswitch will have a sort of plastic nib protruding from its side - pushing that in, should make it click as it operates. You can buy replacement switches for around £1, they are a standard part, but for now I would just buy a new head. Once you have your heating working, you can then maybe spend time investigating/repairing the original head to keep as a spare.

3-port valve actuator seem to be the most common cause of heating system failures, so always worth having a spare to hand.
 
Do you think another brand might be more reliable, or would that require changing the valve type as well?
 
Ordered new Drayton valve & actuator (Amazon sell these cheaper than Screwfix for some reason).

Swapped the motorized valve over, and heating is now firing up. So must have been microswitch.

Incidentally, it looks like the design has changed slightly. Whether it is more reliable, we shall see!
 

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