Heating problem - sludge in 3 port valve?

[redmoorphil]

Hi guys, for the last few days CH system has been playing up. The heating comes on fine, but after a while the downstairs radiators cool down. I thought the actuator on the 3 port valve may be at fault but I have fully tested it today and it seems fine. Also removed the motor box and tried moving the valve by hand - it moves freely but only between the 5 to 12 and 5 past 12 positions which seems to be normal?
Found last night that turning the heating off and then on at the thermostat solved it for a while.
When it cooled again tonight (after about an hour of running) I went upstairs and checked out what was happening. The pump was running fine and the valve was still open for central heating. I turned the heating off and the valve closed and then there was a loud gurgling noise between the pump and valve. Switched it straight back on and the valve reopened and everything started to warm up again nicely.
Because all the electrics seem fine I am leaning toward the valve becoming blocked by sludge which clears when the valve is moved.
I would appreciate any advice before I take any further action on it.
Many thanks.
Phil

 

[herebriefly]

I take it you have a system full of water. No blocked cold feed or empty header tank?

By your comment I assume youve already checked this.

David.

 

[redmoorphil]

Hi David,
I haven't been up to check the header tank but the system is definitely full of water. I've did try bleeding all the radiators and the pump to check this and they were all fine. Also tried the thumb valves and they are also free of air.
There is also a bit of a whooshing noise around the pump and valve which sounds like something travelling through the pipes other than water.
It has now been running fine for a couple of hours after switching on and off, but then it did yesterday too.
Many thanks,
Phil

 

[twgas]

Whooshing (as I know it) is often as a result of a blockage/restriction in the pipework. The most likely suspects for this are,

• cold feed/open vent area,
• pump,
• any valves which may be turned down/off.