Heating system motorised valve questions

[John Smith]

Central heating playing up so I've been checking the valves. Two questions.:

1. The central heating circuit is controlled by a 2-port Danfoss valve. I replaced the motor head a couple of years ago. I've taken it off and got the heating going by turning the valve on manually. But I don't think this motor is faulty - but i've forgotten how you fit it back on. How is it done - what positions do the valve and motor need to be set to.

1. The hot water motorised valve is buzzing loudly (I thought it was the Danfoss, but no). This is a 2-port Honeywell HF 002 body and is now about 15 years old - is this one OK to take off and replace or is it integral to the pipework (getting conflicting info about this).

thanks!

[John Rumm]

I find the easiest way is to get the head onto the shaft first, and then rotate the head into the correct place to get the screws in.

IF its held on with two brass screws (visible once the cover is removed) then its usually fine to take the head off. Some of the older 4 screw versions could not be dismantled in this way IIUC.

[John Smith]

OK thanks. I've now realised it's the old Honeywell that's controlling the rads, so it does need replacing.

I can't get the Danfoss motor to respond though to the hot water cylinder themostat or controller but as we have the hot water on all the time I've left the valve open, and put the actuator on manual-open and not refitted it. Not sure why it's not working.

If the central heating doesn't come on in the morning apart from me being toast I'll have to get the cover off and see what's what.

[Roger Mills]

You need to fix it because, in this position, the HW will be heated whenever the boiler is running for the CH - and may got hotter than desired.

If the actuator doesn't move in response to the cylinder stat when removed from the valve, either the actuator is faulty or there is a wiring fault.

Bear in mind that with an S-Plan system (which is what you appear to have) the boiler will only fire when one or both valves are fully open and operate their micro-switches. If the HW actuator isn't working, *it* won't make the boiler fire - and you will rely on the CH actuator firing it.

If the CH actuator ain't working, it won't! If it's just noisy, it may still be working ok. If it has opened the valve, the manual lever will move freely with no resistance.

[John Smith]

Good point - thanks.

Yes it's an S plan.

It came on this morning so I wasn't toast. I will take the cover off later and see if it's the model that doesn't need drain down - any one looking there's a good video on the Honeywell here:

And and even better one on how these things work here (using a Drayton as a model):

[John Smith]

Roger - just a follow up question then:

So the hot water isn't coming on automatically.

It does come on when I open the valve manually with the programmer switched on so I presume that's triggering the microswitch and firing the boiler.

What is the best fault finding squence for this - the components are:

Honeywell progammer Hot water cylinder thermostat Danfoss motorised valve

All wired into a wiring block.

I replaced the Danfoss actuator a year ago but at present the motor clearly isn't active but I can't beleive it's gone after a year?

[John Rumm]

Does the motor move if disconnected form the valve body?

Best thing to do is to identify what setup you have from here:

Then follow the circuit through from the programmer end to the boiler, with a multimeter and see how far the signals you need get.

So say you decide you have classic S plan wiring:

Start with the programmer calling for DHW on and CH off. Check pin 6 in the wiring centre is live. Now rotate the cylinder stat so that you can hear it click in each direction and check that pin 8 goes live in sympathy with the stat position. Check the DHW valve moves in response to the demand. Check pin 10 (orange wire out of the valve) goes live when the valve is open. Check the call for heat goes live to the boiler / pump.

At some point in that procedure you will likely find something not working. (often the valve not moving, or not moving enough to close the microswitch that feeds a demand to the boiler)

[Roger Mills]

Yes, that's a pretty comprehensive description of what the OP needs to do. Chances are that the problem is with the actuator motor - even though it's already been replaced - but it could be the programmer or cylinder stat or any of the wiring. Following this sequence should enable it to be diagnosed.

[John Smith]

Thanks both. Latest is that PCB on boiler blew a fuse and knocked the system out. Probably something I did. But up and running now.

[John Rumm]

Does the boiler provide a controlled output to drive the pump[1]? If so a short in the wiring feedin the pump could do that.

[1] Many system will differ from the standard S plan wiring with the boiler switching the pump supply itself rather than it being powered automatically when the call for heat goes to the boiler. That way it can do things like timed overrun.