Central heating problem

[trevorn]

Have Potterton Suprima 60 boiler, Landis RWB9 programmer, Myson CP53 pump and an acl/lifestyle 22m mid-position valve.
All was working OK until a few weeks ago.
Hot water is fine, but radiators are either cold or tepid. Pipe from valve to rads stays cool even when programmer is calling.
Plumber suggested valve assembly replacement as he thought the motor may have blown and it was awkward to get at. Quoted £247 + vat.
Declined this offer, and managed to replace motor(Synchron) myself. Still not working. Manual switch on side of valve has never worked (noticed today that it has sheared off), but assume that the motor should still open valve when called to.
I can open the valve by easing the spring back in the valve assembly, and the rads then heat up. Tested the motor by lifting it out of assembly - but it doesn't spin at all when CH is called from programmer.
Not sure what to look at next. Any ideas ?

 

[brumylad]

test the wire going to the motor is delivering power. use an appropriate multi meter while changing the settings on the programmer. Don't electrocute yourself.

 

[kevplumb]

check the roomstat isnt turned down

 

[MANDATE]

Hi Trev.! A couple of points. Remove the valve head and observe the action it takes when you have HW only--HW/CH --CH only, you should see the part that engages with the spindle move to the correct postions according to which you have selected. The motor does not spin as implied, the total movement from HW through to CH is only 90 degrees. Think of it starting in the HW positon with the spring applying little tension, now when you select the next stage HW/CH the motor drives it just 45 degrees overcoming the spring tension, until the first micro switch is activated. It does not move any further because the supply voltage has been reduced so it is held in equilibrium at the mid position. Now when you select CH only the supply voltage is raised again and the motor continues another 45 degrees when it comes up against a stop.When the supply voltage is removed or reverts back to the reduced amount the spring returns the motor to the start position (HW) or the mid position (HW?CH).
The second point is with respect to the valve spindle, this may have become stiffer to move and may need WD 40 working in to make it easier to move. It probabley has not been in the CH position during the summer.
Don't forget the motor has to overcome the strengh of the spring as well as any resistanceof the spindle, so it may not be moving the full 90 degrees or even the 45 degrees to get to mid position.
If necessary the spindle could be removed for cleaning but it would involve some draining of the sytem.
I think a new motor is around £15 and a new actuator head if you can get one will be around £50.
Hope it helps