Hot water but no central heating

[gates1979]

my hot water is working fine but my central heating wont come on. I have moved the arm on the 3 port valve to as far as it will move and the boiler fires up and the rads start to get hot but as soon as I let go or lock it in the manual position the boiler goes off and the rads cool down

 

[CM25]

When u moved the arm was the hw on? If not sound's like the motor in the 3 port head has gone, if it was most likely be prog, room stat, 3 port head

 

[SafeGasInstall]

Time for new one ,

 

[gates1979]

Yes the heating was switched on the programmer, also if I held the arm and got someone to move the room stat it came on when the stat called for it so does that rule out the stat being faulty

 

[gates1979]

Sorry the heating was switched on and the hot water was off

 

[R1CKY]

Hot water but no heating is a classic sign of a failed synchron motor in a three port. Most three ports spring return to the hot water only position when there is no demand, selecting hot water only doesn't operate the motor in the valve, it simply switches on the boiler and pump.

For a short time fix, if you lock the lever in the open position you'll have some heating whilst the cylinder is calling for heat.

 

[CM25]

Yes sounds like the motor chap