central heating failure: ? diverter valve fault

[mervington]

Our central heating has a Honeywell ST64OOC timer/programmer. We only use both the hot water and central heating controls at off or continuous. The diverter valve is the Honeywell V4073A.

Last week, the radiators would not get warm/hot except when the boiler was supplying the hot water system. Switch the hot water control to off, and the boiler would stop, even though the central heating control was on continuous and the radiators were cold.

We have a contract with Worcester-Bosch. The engineer came. He said there was no electrical supply to the boiler for the central heating. Our contract relates only to the boiler. He said the fault could be with the wall thermostat, but more likely the diverter valve.

I asked a local plumber/heating engineer to look at it. Apart from turning things off and on, he did not really check anything.

He said - and this is the real issue/question for the forum - that the boiler could not operate for central heating unless the slider switch for the hot water was also at continuous. I told him I did not believe that since we used both seperately, but he was adamant. He got the system "working" again by increasing the setting on the cylinder thermostat. However, we only have central heating when the boiler is supplying the hot water cylinder. As soon as the cylinder temperature is reached (or we switch the hot water off), the central heating also goes off.

I think the "physical" side of the diverter valve is working, but it it failing to provide an electrical supply to the boiler - perhaps a micro switch or something?

Advice/views would be much appreciated.

Thank you.

Mervyn

 

[seco services]

when the heating is on/calling and the hw is off or satisfied check that you have power on the grey wire, and orange wire.

sounds like the micro switch is faulty. as the valve is opening so that proves the motor is working.

 

[mervington]

Thanks seco services.

I have a complete new diverter valve on the way. I thought to change just the power heads might be a good start?

Mervyn

 

[MANDATE]

Just remember that when HW and CH are both switched off the 'grey' wire of valve is still live, so its important that all power to boiler is removed when changing a actuator head.

 

[mervington]

Thanks mandate.

I will switch off the boiler completely.

I'm still mystified why the heating "engineer" who called could conclude that the CH would not function without the HW also being switched-on. I thought I was going mad............ I questioned him several times but he remained adamant.

Mervyn

 

[seco services]

probably don't know the difference between a gravity hw and pumped hw system

 

[mervington]

Thanks seco services.

I've now undertaken the test. The grey is fine. No voltage on orange. I've got a new unit, but it will be tomorrow before I can fit the powerhead from it.

The advice note refers to the position of the "arm/lever" when undertaking the changeover. I take it that it should be locked in the indent on the plate where it says man open?

Thanks for help - much appreciated.

Mervyn

 

[MANDATE]

My understanding is the arm/lever should be locked in mid position for filling purposes only, which means both ports are half open and will prevent air locks.
When you remove power from the boiler to change the actuator the valve will return to the rest position which is HW due to the return spring.
Based on this I would say the replacement head would also need to be in the same position so there would be no need to lock head to mid position.

 

[mervington]

Thanks Mandate.

I've now found the Honeywell instructions on the net. They say -

When making a like for like replacement of the powerhead only, ensure that the Auto/Manual lever on both the installed and replacement heads is in the Manual position.

Thanks for all the help.

Mervyn

 

[mervington]

I've replaced the head, and all is now well. (There were white marks on one of the micro switches - presumably arcing).

The only problem was removing one of the retaining screws. The original installer had put the diverter valve assembly hard up against the wall. Just about impossible to see the screw head, let alone get at it. I manage to loosen it after modifying an old screwdriver.

Now if Honeywell had used screws with positive location rather than a straight slot, all would have been very easy.....

Thanks again for help.

Mervyn