Cen Heating only works by manual operation of 3 way valve

[Stagman74]

Advice please:
I have a conventional heating system from the late 80s - boiler, hot water tank and radiators. This is controlled by a timer (acl switchmaster), room thermostat and tank thermostat (both are the original Sunvic units). With the timer's controls set to Heating and Water, I can only get the heating to come on if I manually operate the Danfoss 3-way valve. Even if the hot water is fully up to temperature, I have to manually pull the lever to the position where the pump starts and the boiler fires up. I don't believe the Synchron motor is at fault. I have replaced this and it made no difference; the old motor also appeared ok when checked with a multimeter. With the actuator removed, the 3 way valve moves easily with just 'finger' force.
The current actuator was fitted in 2007, but it is set on the original Sunvic valve and baseplate.

Should I consider replacing the whole actuator (Danfoss p/n 5933)?

If so, which one is recommended as the 5933 appears to be no longer available?

Could this be a faulty thermostat issue or even the timer? If so, how do I check?

Many thanks in anticipation.

 

[jackthom]

As a starting point you need to check whether the 230V (to activate the synchron motor) is arriving at the Danfoss valve from the room thermostat.

If you don't have a multimeter you may at least be able to hear the motor operate when someone else turns up the room thermostat.

There's a fair chance it's at least partly motoring but a dodgy microswitch or other missing voltage on the actuator could be preventing it getting right across to the heating-only position.

 

[Stagman74]

4 wires to actuator:

Brown/white wire connected to 'actuator'.
Blue wire connected to Synchron motor.
Grey wire connected to 'actuator'.
Orange wire connected (return from?) to Synchron motor.

Have put multimeter across the Brown/white and Blue wires. Reading of ~240V recorded.

Hope this is correct.

Thanks.

 

[MANDATE]

Or it could be like one I had. It motored across to the CH only position and still did not light the boiler.
logic suggested a micro switch at fault. Decided to replace the whole actuator head, problem solved!.
Later dismantled old head. Identified the relevant micro switch which was a soldered in type. tested it and proved it faulty, then managed to remove the side to find dirty/burn't contacts which I cleaned up and bench tested.
Now have spare head for future.
There are in fact two micro switches in the head, so 4 sets of contacts.
One set relates to power from room stat to the motor (first half of range)
One set relates to power from programmer HW OFF and also the cylinder stat to the motor (second half of range).
If any of the above two sets fail to make contact or break contact it will affect the movement of the motor.
A replacement head is the best solution, or a replacement valve

 

[Stagman74]

Thanks for the prompt reply.

My next step would appear to be a new actuator.

Wickes has a 3 Port Danfoss actuator (Wickes Code 228352) which I assume is a replacement for the Danfoss P/N 5933, Type HSA3 as presently fitted.

I will hopefully buy this tomorrow and fit it unless anyone has any other views, or knows that this actuator is not suitable for my set up.

 

[MANDATE]

4 wires to actuator:

Brown/white wire connected to 'actuator'.
Blue wire connected to Synchron motor.
Grey wire connected to 'actuator'.
Orange wire connected (return from?) to Synchron motor.

Have put multimeter across the Brown/white and Blue wires. Reading of ~240V recorded.

Hope this is correct.

Thanks.

A modern valve basically has 5 wires.
One is earth 'yellow/green' no explanation needed

One is neutral 'blue' required wherever there is a electrical load 'motor'

One is power 'white' from room stat. It drives motor through 1st M/S and it also supplies power to 2nd M/S to feed a PCB and an output to light boiler

One is power 'grey' from both programmer HW OFF terminal and cylinder stat 'satisfied terminal' This power drives motor from mid position onwards.

One is power 'orange' from the valve to fire boiler.

power on grey present when either HW is OFF, or when HW is on but has been satisfied

 

[Stagman74]

With controls set for CH:

Multimeter readings as follows:

Blue - Brown/white ~240V.

Blue - Grey ~240V.

Blue - Orange ~ 0V.

Hope this makes sense.

 

[MANDATE]

Yes it makes sense.
With CH on of course there should also be 240v on the 'orange' and the boiler would be fired up.
So having ruled out the motor, one of the micro switches is faulty,

M/S 1 if faulty could fail to switch power to drive motor on either set of contacts.
M/S 2 if faulty would fail to switch power from 'white' to 'orange' to feed the boiler.

 

[Stagman74]

Thanks Mandate.

Final question(s) before I depart for the day:

With actuator manually operated in order to fire up the boiler, I still get 0V between Blue and Orange with the boiler running. Is this what would be expected?

Also the hot water works fine and once you have manually operated the actuator, the CH does appear to be working on the room thermostat. The only issue is if you make demands on the hot water, the actuator returns to the HW position and then won't return to CH once the water is up to temp. Again is this what would be expected?

I'll proceed to order an actuator from Wickes, but it's going to be a few days before I fit it and then provide an update.

Many thanks for your advice and help so far.

 

[MANDATE]

Thanks Mandate.

Final question(s) before I depart for the day:

With actuator manually operated in order to fire up the boiler, I still get 0V between Blue and Orange with the boiler running. Is this what would be expected?

Also the hot water works fine and once you have manually operated the actuator, the CH does appear to be working on the room thermostat. The only issue is if you make demands on the hot water, the actuator returns to the HW position and then won't return to CH once the water is up to temp. Again is this what would be expected?

I'll proceed to order an actuator from Wickes, but it's going to be a few days before I fit it and then provide an update.

Many thanks for your advice and help so far.

The lever is provided to latch the valve in mid position when filling to prevent air locks.
So when you use it you're only moving the valve to mid position, now that would suggest the first set of contacts in M/S 1 are not making contact, otherwise it would not need to be over ridden.
If you have selected CH only then the grey wire would drive the motor forward from mid position, that is providing the second set of contacts in M/S 1.
When CH becomes satisfied the valve does not drop back, it stays at CH only, held there because the grey is still live. All that happens is the room stat cuts off the power to the white which feeds the orange, which feeds the boiler.

It's a bit more confusing when you have HW and CH together.
The valve is required to be in mid position, until one of them becomes satisfied. So the grey must not be live, so it can't send the valve on from mid position.
Also when HW is selected, either on its own or together with CH the boiler does not get power from the valve.
Power comes from the programmers HW ON terminal and goes to the cylinder stat, which it can't do if HW is not on.

Now the mid position is not fixed, it's a temporary position until either HW or CH becomes satisfied and when that happens, one of the stats operate resulting in the valve moving to give full flow to the not satisfied side.

If CH became satisfied valve would move to HW, but when CH became not satisfied again it would move back to mid position, except I believe in your case it cant ,because of the M/S.
If you can remove the head off the spindle, its easy to see what happens or what doesn't happen.
HW only motor will be in rest position or unwind to rest position.

HW with CH added providing they both in demand valve should move to mid position.

Turn HW off leaving CH only and valve should move to CH only position (and making the orange wire live)

 

[Stagman74]

Thanks Mandate.

In my case I have on the programmer either HW or HW and CH together operating what appears to be a "Mid Position Valve".

With HW selected on the programmer the actuator is at rest ie unwound. All appears to works fine ie HW is brought up to temperature and then kept at the temperature set on the tank thermostat.

If I switch to HW and CH then the motor / actuator does move, but only a very small number of degrees; this does not light up the boiler and it appears not to permit water to flow around the radiators - certainly it is not being circulated by the pump. I have to then use the level to manually turn the motor and achieve the full 90 degrees of movement to the valve which then ignites the boiler and starts the pump. At this position the lever then latches with the valve set such that all the flow is going to the radiators.

From the detail you have provided I appear to have a faulty actuator or at last a M/S within it. Is this your view too?

 

[MANDATE]

You've eliminated the motor, you've got the 240v on both white and grey.
Nothing on orange when it should be 240v.
It's got to be a micro switch problem.
It either does not move over first half or it does not move over second half due to faulty contacts in M/S 1.
Or if M/S 1 is not faulty and it does move and there is no voltage output from the orange wire then its due to faulty contacts in M/S 2, or the micro switch is not being triggered
With no output on orange I know of no other explanation

 

[Stagman74]

Mandate,

Many thanks for all your help and for so logically laying out the conclusions from the tests that you advised I perform.

I have replaced the complete actuator and all appears to be working fine now.

Regards.