Pump or Motorised valve probably not working - help!

[MarkS100]

My central heating system is causing me problems. The boiler fires OK, but I can only get hot water. The central heating comes on for a few seconds and then the boiler switches off if I program it just for CH.

The pump seems to be working, well it is making pump like noises! (it’s a Celsia Multi Head). The programmer is a Lifestyle LP112 and is not that old.

I took the circuit board out of the 3 way motorised valve (I was convinced this was where the problem was), but nothing looked obviously wrong and the motor turns the valve as far as I can tell. The micro switches seem to be OK. The valve is an ACL-Drayton 679H340-30LO

Is there any way I can test the valve/micros switches operation - preferably without unsoldering them from the circuit board! The spindle in the valve seems to move OK. Can I actually test the pump? (which I am now beginning to suspect)

I have drained the system twice. Frustratingly I managed to get it going last Sunday, but since then it has resolutely failed to work properly.

Any suggestions would be gratefully received.

Many thanks,

Mark S.

 

[jackthom]

Hi do you have a multimeter and are you OK measuring mains voltages?

For CH by itself, the orange wire from the 3-way valve actuator should go LIVE when the valve has motored right over to the CH_Only position. It's this which should fire up the boiler/pump.

 

[MarkS100]

Thanks. I'll check out your suggestion, however the bolier does fire, but switches itself off after 10 seconds or so. It's as if it is overheating - I don't think the water is getting through the CH circuit correctly.

 

[MANDATE]

The pcb within the actuator head is not related to CH only. It is there for the situation when you select both HW and CH. It provides a modified voltage to hold the valve in mid position against the opposing pressure of the return spring. That of course is not a permanent arrangement, It's just till one of the modes gets satisfied and then the valve either drops back to HW only or moves forward to CH only.
The valve has no active role when HW only is selected other than the spring returns the valve to the 'rest' position, which is HW.
To get CH only, the valve operates over two sections. The programmer provides power to the room stat, then the room stat provides power to the white wire of the valve, this drives the motor to mid point only.
A second source of power is provided from the programmers HW OFF terminal to the valves 'grey' wire.
When the first microswitch is triggered, it cuts the power from the white and it takes the power from the grey. This drives the motor over the last section and at the same time triggers the second microswitch which allows power out from the orange wire.
It's highly likely that valve is not moving (due to faulty motor) or if it is moving, it may not be moving far enough. It could be that it is moving ok but the second micoswitch is faulty.
Of course theres also the possability the room stat is at fault and this should be checked first. ie power on the white.
And also check power on the grey when HW is off.
The functioning of the valve is not easy to understand, but I hope this might help.

 

[jackthom]

Thanks. I'll check out your suggestion, however the bolier does fire, but switches itself off after 10 seconds or so. It's as if it is overheating - I don't think the water is getting through the CH circuit correctly.

I don't suppose theres a temperature or error display on the boiler?

 

[kevplumb]

what is the boiler

make / model

 

[MANDATE]

What happens when you select both HW and CH?
If HW happens to be satisfied, either increase the cylinder stat or run off some hot water, this will create a demand for HW and boiler will light cause the power to light it come from the cylinder stat.
In this situation the valve should move to mid position and both the cylinder coil and radiators should get hot. If they do it will prove there is no blockage on the CH circuit and the pump is operating.
However sometimes pumps can be misleading. I removed one for examination and found the inlet and outlet port reduced (by silt)from 20mm down to about 7mm , it was the obvious reason why hot water was not being circulated through a radiator that was furthest away

 

[MarkS100]

From memory, when both CH and HW are selected the valve the goes to the mid position, but we still only get hot water. I'll try out some of the other suggestions as well. I think the actuator motor in the valve is working OK, but I'll check again.

I did try and take the pump to bits, but the isolator valves either side don't seem to be doing much isolating, so I just got quite a bit of hot water before I could screw it back together again. Looks like I'll need to do at least a partial drain down to investigate further.

Thanks for all the suggestions to date - I really appreciate the input.

 

[MANDATE]

There are two types of isolation valves.
The gate type does not always fully close and the ball type sometimes leaks a little on the spindle ( 'O' ring ), but if you decide to replace the pump, I would suggest you replace the valves as well

 

[MarkS100]

Just to say thanks to everyone who replied, te input was very useful.

I managed to check off all the components in the system - I took the pump to pieces and discovered the impellor was full of cotton thread or string, so although it was spinning it was not pumping any water, hence no CH warmth. I sorted that out.

I also cleaned out the header tank very thoroughly, topped up the system and now it is fine, and also significantly quieter than it has been for a long time. I guess the pump is running much better and hence very little vibration.

Now I only have to wait for the boiler to conk out!