Central heating constantly on

[LordFrederickIII]

This is the setup of the central heating:

Two theromostats (one for upstairs and one for downstairs). Both linked into a digital controller which allows control of the central heating and water heating. The water heater is an unvented water cylinder.

Two Viessmann Vitodens 100 work in tandem to heat up the house and water. There's also a water pump attached.

Up to yesterday our central heating was working fine. Woke up this morning to find the whole house was roasting hot. Thought someone had left the thermostats on max, but both were was set at 18c whereas the house temperature was 24c.

Initial thought was the thermostat is sticking, but even after fiddling about with them, heating still on.

Then turned off the digital controller which should cut out all demand to the boilers. Heating still on.

Tried a reboot by switching all power off, still got the same problem.

With the thermostats set to zero and the digital controller off:

If I go to a cold radiator (i.e. one where the themostat is set to 0) and turn it up, the radiator becomes quickly hot.

Checked both boilers, and temp is at about 60c on both. The gas dial on the gas meter is turning.

Any ideas on what it could be? Boilers are coming up to a year old

 

[Whitespirit66]

Poss problem with the 2 port valve for the heating - may be jammed on. When you turn the heating on and off at programmer, does the valve operate?

Untitled

• Whitespirit66
• 4 Feb 2013
• 4

 

[LordFrederickIII]

Poss problem with the 2 port valve for the heating - may be jammed on. When you turn the heating on and off at programmer, does the valve operate?

Untitled

• Whitespirit66
• 4 Feb 2013
• 4

I just had a look. I have three of those. One is marked with 'upstairs heating', the other with 'downstairs heating' and the third with 'hot water'

All three have a lever on the side. If I pull the lever it seems to wind something and then come back into the original position. That happens on the upstairs and hot water one.

The one marked downstairs does nothing if I pull the lever. I.e. The lever moves but just stays at the new position rather than returning to the previous position. I can't feel any resistance on it either whereas I can with the other two.

 

[Whitespirit66]

With the downstairs heating off the 2 port valve for downstairs should be unpowered and at rest. In this state, you should be able to move the lever to the other side, feeling resistance as you push it. It should then return to the original position when you let go of it.

If this doesn't happen, the valve is poss jammed. May need an actuator head replacement.

 

[LordFrederickIII]

Is it a straight forward diy job to replace?

 

[Whitespirit66]

Is it a straight forward diy job to replace?

Not difficult. Just remember that these valves have a permanent live supply, even when ch is off. You will need to turn the heating system's fused spur off and remove fuse. Then remove cover and screws holding actuator to valve. Swap wires one at a time in junction box.

 

[LordFrederickIII]

Does anyone know if the value head from a Honeywell 22mm interchangeable with one from a 28mm?

 

[Whitespirit66]

Does anyone know if the value head from a Honeywell 22mm interchangeable with one from a 28mm?

Yes, they're compatible.

 

[twgas]

The 28mm valve will have an extra, white, wire. This should be made safe ie. put in a spare connection in wiring centre/junction box.

 

[LordFrederickIII]

Thanks for the help chaps. Did it all today in about an hour. Shouldn't have taken that long but there were three valves all wired together in a junction box. Wasn't particularly happy with some of the existing wiring so ended up sorting that out as well.