Three way valve needs replacing?

The Danfoss HSA3 three way valve is playing up on my elderly dads heating system, which it has done before but this time I cant get it to run normally.

Previously I have taken the actuator off and lightly lubricated the mechanism which has worked, but not so this time unfortunately.

Last time it played up the CH rads were heating up when the boiler was heating DHW, but now the DHW will not heat up whatever setting the programmer is on. The CH works ok as programmed along with the room stat.

With the actuator off the valve assembly, the valve spindle turns ok by hand and I wonder if it could be the actuator only that needs replacing.

Can anyone offer any ideas, thoughts or comments please?

Any help appreciated.

Sounds like the head though it's an odd fault. Could be a faulty cylinder stat or programmer. Wiring diagram + meter required for diagnosis.

Thanks for the reply.
If it helps to diagnose the fault, with the programmer set to CH off and DHW on, the boiler heats the rads only, but if I turn the stat down on the HW cylinder the boiler goes off.

From posts on this and other forums it seems the cause could be either:

1) The HSV3 three way valve body that has failed.

2) The HS3A Actuator has failed.

3) The Synchronous Motor in the Actuator has failed, or I`m hoping you guys in the know can advise further.

Before my dad calls out a heating engineer at a cost he cant afford if I can try different things it`s obviously worthwhile. I can buy any of the parts above from screwfix and I`m confident I can fit them myself.

I don't have the equipment to check on the electrics but surely there are other ways to diagnose the cause, through a process of elimination?

Looking at it again this morning with the actuator removed, the brass spindle on the body turns 360 degrees fairly freely. Is this normal?

micktheminer said:

Looking at it again this morning with the actuator removed, the brass spindle on the body turns 360 degrees fairly freely. Is this normal?

Click to expand...

Not familiar with the Danfoss mid-position valve, but that does seem a bit unusual. Most MPVs only rotate a few degrees as the "stopper" moves from port A to Port B.

Is there any "key" which prevents the spindle meshing incorrectly with the actuator? If there isn't: remove actuator, rotate the spindle by 180 degrees, replace actuator.

micktheminer said:

With the programmer set to CH off and DHW on, the boiler heats the rads only, but if I turn the stat down on the HW cylinder the boiler goes off.

Click to expand...

Please check that the valve has been installed the correct way round. Port A should go to the central heating; port B to the cylinder. Ports are labelled on the brass body.

Thanks for the reply.

The spindle has a flat on one side that engages with the same shape slot on the actuator so it cant be engaged wrongly.
The A & B ports have been in the direction you mention. The system was installed some 7 years ago without any probs until last summer when the valve was letting by to the rads while programmed for HW only.

Then I took the actuator off, lubricated the cog wheel with 3-in-1 aerosol and rotated the valve spindle by hand in case it was stuck and its been ok since.

What I`m trying to find out is if and how I can eliminate one by one the various components to identify which one needs replacing.
At the moment I`m thinking its the actuator that is faulty and needs replacing?

New actuator head required, around £60 to buy, 5 wires inc Earth to connect.

Have to do loads of these. (If it helps, I have Danfoss at home , and change the head every four years or so)

DH

That sounds quite frequent, or is that normal ?
Our mpv is Honeywell and in over 30 years it's only been changed the once.

75pete said:

That sounds quite frequent, or is that normal ?
Our mpv is Honeywell and in over 30 years it's only been changed the once.

Click to expand...

Normal for Danfoss it has seemed over the years.....

Dh

Many thanks to all for your help.

With the actuator head off the valve but still wired in, the "key" hole where the valve spindle locates turns when the programmer is switched from ch to hw and vice-versa and seems to settle in the mid position when both are programmed a the same time.
When on the valve and "underload" this may not happen?
But does this still indicate the actuator needs replacing?

Would a new actuator come pre wired as the wires are soldered on this one?

Yes, it will come with cable attached.

Three port motorised valves return under a spring force to the default 'hot water only' position when at rest (de-energised) Then when hot water is set 'on' at the programmer, the operation of the boiler is carried out by the cylinder thermostat.

From rest, when the valve is powered up, as required, it moves to either the central position (heating and hot water) or winds fully across to the central heating only position whereby the hot water port is completely closed off. If you are not getting any hot water that would suggest that the valve is in the central heating only position, ie fully powered up and closing off the hot water port.

To get the valve to that position you would normally need a 'hot water not required' signal on the grey wire to the motorised valve. This comes from two sources. From the programmer when the hot water is set to 'off' or from the cylinder thermostat when the water in the cylinder has reached the set temperature.

As ChrisR has already said this is an odd fault, because normally a failed valve sits at the hot water only position, not the central heating only position as would appear in your case. My first thought would be that either the cylinder thermostat or programmer were stuck on hot water 'off' but from one of your posts, it does seem as if the cylinder thermostat is working.

You can check the basic operation of the valve by removing the powerhead from the valve body and note the position of the spindle with just hot water to be 'on' then also switch on the heating and it should go to the centre position, leaving the heating on, turn the how water off and see if the valve moves further on to the far end of its travel.

This does sound unusual and probably will require detailed tracing of the control signals to be sure. If it helps, you can find a very useful diagram, by clicking here. This shows what should be happening depending upon the status of the system. Look at the 'Y' Plan diagrams.

I`m hoping someone can help on this. After several problems I want to replace the 3 way valve and actuator and have bought a Danfoss replacement pack of 3 way Valve Body, Actuator, Programmer, Cylinder stat, Room stat and wiring box as the whole pack was cheaper than buying just the valve and actuator.
My question is: the c/h-rad system is a sealed system but the dhw is from an open tank in the loft and a cylinder in the airing cupboard and when I drain the c/h-rads to remove the valve do I need to drain the dhw tank and cylinder as well?

Grateful thanks for any support on this.

No, the DHW is completely separate from the water circulating around the boiler system so you don't need to turn off the hot water header tank valve.

Before starting are you fairly sure the CH system is not open vented but is a sealed one? The boiler should have a pressure display and a filling loop.

(if it isn't sealed you'll have to locate the smaller feed & expansion tank)