Central Heating and Hot Water not working properly together

[drussella]

Question on hot water and central heating not working correctly. Standard heating system - gas boiler, timed clock switch, no room thermostat, mid position valve. Turned on heating couple of weeks ago after the summer and everything worked fine. Then heating stopped working. Covered by BGas cover so engineer called. First he said it was loose connecitons in the Mid-position valve - fixed it and it ran. Next morning didn't come on. he came back - couldn't find anything obvious - got it working and left , promising to call us after 2 days to see what was happening. Again didn't work that night or following morning. He called today and is coming again Friday.

Wanted to run these symptoms past the group to see if they made sense and you could advise , so I can gently point him/BGas in the right direction - he didn't inspire confidence previously when he didn't try all options.

After couple of trials I think I've figured these are the symptoms.

1. If hot water is timed to come on before heating then heating doesn't work.
2. If heating is timed to come on before hot water than heating DOES work and so does hot water.

Mid-posiiton valve seems to move to all the right positions when taken off the pipe and tested using the different settings on the times i.e. CH/HW on/off etc.

I've proved this last night and this morning.

Since I'm not mending it myself I'm not going to get into fine details but was after guidance more than anything on whether me interpretation would be feasible. Cheers....

[Set Square]

Well, from what you say, the boiler works and the pump works - so the problem almost certainly lies with whatever is telling them (or not!) to come on.

In the CH-only mode, the mid-position valve plays a *major* role in controlling the system. It is a microswitch inside the actuator which operates and turns the boiler and pump on once the valve has motored to the CH position. If this doesn't happen - no heating!

There are several reasons why this may not happen correctly:

• Duff motor in actuator (in your case, this seems ok)

• Seized valve - This is a possibility. If the valve is seized or stiff, the motor may not be able to move it even if the motor seems ok when the actuator is removed from the valve

• Duff microswitches in the actuator

Either way, the solution is straightforward:

• Make sure the mechanical part of the valve moves freely. You should be able to rotate the shaft with finger and thumb or, at any rate, with *light* pressure with a pair of pliers. If it is seized, free it or replace it

• If the valve is free, and the system still doesn't work properly, replace the actuator

[drussella]

Just to complete this - the engineer diagnosed the fault as something in the timer itself - replaced with a new one and it all works...