Slightly unusual question regarding motorised valve.

macson19 · 16 Feb 2020

Hi all, I have the common problem of heating working fine but hot water only warm. I know the usual places to look starting with the 3 port valve etc. However having changed the valve and flushed the system problem remains. What I have noticed and worked out is the motorised actuator at first appears to do what it should. However if i run hot water only it heats up fine. If I have it on both hot water and heating radiators it fails to heat water tank (sealed) much. This is why I first thought it was the valve itself (valve not shutting properly)
When it is on radiators only the lever is fully across as it should be. However when I turn hot water on although the lever moves to the mid position as it should it only moves just over a third of the way rather than half way.
My question is should it move all the way (it is a Danfoss HS3, 14 years old) to the half way point and if this is the cause of water bleeding towards the radiators rather than the hot water tank would I need to replace the whole motorised part or just the synchronous motor? The manual lever moves with the motor/spring as I believe it should other than not returning to the centre when hot water/radiator called for. Or do I need to look elsewhere such as possible old weak water pump (my next port of call if not the motorised valve) ? Any help would be most appreciated.

kidgreen61 · 16 Feb 2020

Take the actuator off and see if you can operate the spindle easily.
Then, with the pipes cool, turn on the heating, turn the spindle to HW and see if heating pipes warm up, if they do, then valve is goosed.
If the spindle is stiff, then replace valve.

D_Hailsham · 16 Feb 2020

The end lever is not a reliable indication of how far the valve is open. This is because it is not attached to the spindle. This is demonstrated by the lever being 'loose' in the slot when the valve is open to heating.; The lever is only there so the valve can be be opened manually, e.g when draining or refilling the system.

Apart from a stiff spindle, the symptoms you describe are typical of an incorrectly balanced system. The heating is taking more than its fair share of the water circulating.

macson19 · 16 Feb 2020

I replaced the valve for a new one a couple of weeks ago thinking it was the 'ball' in the valve that had worn out. Turned out it was a valve with solid metal cylinder thing that rotates ( can't describe it very well) The point being it did not appear worn out but had a new one (same design) so put new one on anyway. So pretty sure it's not the valve (at work so can't try the above experiment but will later just to check). Incorrectly balanced system sounds more likely but don't know how I could correct that?

macson19 · 16 Feb 2020

By balanced do you mean balance of the radiators or easier run for the water to head off to the radiators rather than the hot water? Radiators reasonably balanced and haven;t changed configuration of radiators for some time (added a small radiator a couple of years ago but didn't have this problem then).

ianmcd · 17 Feb 2020

Post a pic of your HW cylinder showing the pipework, it was quite common to fit a restricting valve on the indirect coil outlet to balance the flow of the heating and the HW, it could just be that needing adjusting if you have one, if the rads are heating fine there is nothing wrong with your pump

ericmark · 17 Feb 2020

There are two three port valves one for W Plan and one for Y Plan the W Plan has no mid position, so likely Y Plan valve, at rest it is domestic hot water only, half way both and all the way central heating only, in the rest position and mid position the boiler is fired up direct from the tank thermostat, only when fully over is the boiler powered from the orange wire from motorised valve.

So with DHW only the valve should not move. There are two input wires to valve white and grey, the white is energised when central heating is required, the grey however is energised when domestic hot water is NOT required, it has been years since I worked on a Y Plan, but I remember with a meter I had a problem working out what was going on, there are diodes and resistors inside the valve which give some odd results.

Removing grey wire should cause the valve to only go half way but can't see what would cause grey wire to be powered when hot water is called for?
However if white wire was always powered then valve would not return to rest position. However to test likely the easy way is switch off, which means valve will go to default DHW position, then unclip head and switch on DHW and see if the valve head moves which is should not, and the DHW should work.

Most likely fault from what you have said seems to be a wire in the wrong place.

D_Hailsham · 17 Feb 2020

ericmark said:
Most likely fault from what you have said seems to be a wire in the wrong place.

If you read the OP's first post carefully you will see that the valve is working exactly as expected. The only problem is that, when in mid-position, there is insufficient flow through the cylinder.

macson19 · 17 Feb 2020

Working today and tomorrow but will test/take closer look Wednesday to see if I can figure it out based on above advice etc. Thanks for your input and I'll see what I can find - don't think there is a restricting valve but will look.

Hugh Jaleak · 17 Feb 2020

Another possibility is the cylinder coil is partially restricted, sludge or much blocking it. I'd say normally the path of least resistance would be through the cylinder, (the reason a restriction was put into the HW side, to prevent the cylinder taking the lions share of the flow if both CH and HW were calling for heat.) If system is set to HW only, how long does it take for the cylinder to heat up?

Mottie · 17 Feb 2020

macson19 said:
it fails to heat water tank (sealed) much.

Do you mean an unvented hot water cylinder? I only ask because when I had my system converted to unvented, they removed the three port valve and replaced it with two twin ports as they said I shouldn’t have a three port valve with an unvented cylinder.

ianmcd · 18 Feb 2020

Mottie said:
Do you mean an unvented hot water cylinder? I only ask because when I had my system converted to unvented, they removed the three port valve and replaced it with two twin ports as they said I shouldn’t have a three port valve with an unvented cylinder.

You can have a three port valve with an Unvented cylinder , but regulations state that you have to also have a two port as a safety mechanism, that would close in the event of the cylinder getting too hot, and remove the heat source

macson19 · 18 Feb 2020

It's unvented with a 3 port but it's on a boat so regulation kind of goes out the window. Will use the old valve I took off to match up against the movement of the new valve spindle to see how open the valve on each port is in each different position, and a general play around tomorrow. Thanks for all your input.

ianmcd · 18 Feb 2020

macson19 said:
It's unvented with a 3 port but it's on a boat so regulation kind of goes out the window. Will use the old valve I took off to match up against the movement of the new valve spindle to see how open the valve on each port is in each different position, and a general play around tomorrow. Thanks for all your input.

An unvented cylinder on a boat ? please post some pics

macson19 · 20 Feb 2020

Hi all. couple of pics - system on boat: water in tank goes into pressurised system via pressure switch keeping it up to 3bar which is water to taps. There is another valve to the heating system with an expansion tank at 1 bar, hence the unvented hot water tank (no pic as it was ****ing down so didn't go out to the engine bay)spent the morning testing system. Anyway, I put the motorised actuator on the old valve so I could see what was happening to the valve as it wasn't hooked up to any pipework. On the mid position the valve opened both sides - picture of both ends - so it seems motor/valve doing what it should. Can only think there must be a build up of sludge as with both valves open the path of least resistance definitely heavily favours the radiators. Would a weak pump have any effect? I only ask as a couple of years ago the pump (now 14 years old) made a whiny sound. I bought another pump thinking it was giving up but noise went away so never fitted it - it does run really hot. Not sure how hot it should get as it's running hot water through it but if I open my palm and cup it in my hand I can only hold it for a second as it's to hot beyond that?

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Slightly unusual question regarding motorised valve.

macson19

kidgreen61

D_Hailsham

macson19

macson19

ianmcd

ericmark

D_Hailsham

macson19

Hugh Jaleak

Mottie

ianmcd

macson19

ianmcd

macson19

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