No Central Heating only - fine on HW and CH or HW only

[Wildeman]

Are you quite sure the timeclock is not set for gravity instead of pumped?

Checked and it is set to Pumped

 

[Wildeman]

Just been speaking to my neighbour who has been in her house since it was new and her programmer is a Danfoss 102E7 (she said they all had the same as she new someone else at the time in another house with the same programmer - moved on since) so it would appear that mine has been changed to the Sunvic 206XLS at some point before we moved in.

I have attached the installation guide for the Sunvic Programmer and it does state it is a direct replacement for the 102 - can anyone confirm?

 

[D_Hailsham]

The issue I have is that the HW only works without issue and so too does HW and CH until the HW is up to temperature. Once the hot water is up to temperature or CH only is requested on the programmer the boiler fires for a minute or so and then goes out and the radiators do not get warm and cool water is circulated.

The only way I have been able to get this to work is to turn the cylinder stat up to 85 degrees and turn the boiler temp stat down but I have had a shower pump and kitchen tap newly fitted that have a max water temp of 65 degrees!!

Are you saying that you need the cylinder stat at 85 and the boiler stat low for CH only to work? If so, then there is a wiring fault.

Has the electrician checked that the expected voltages are present, depending on the status o the programmer and room/cylinder thermostats?

Was the previous valve also a Sunvic Mo-Mo?

 

[jackthom]

The pictures don't show anything obviously wrong with the layout and at the moment I doubt that the programmer is causing this problem.

If I was there I'd want to look very carefully at the behaviour of the boiler and pump when in CH only mode while monitoring the voltage supplied to both.

Does the pump run and does it definitely keep running after the boiler goes off.
Is the boiler switching off because it is quickly overheating?
You say the pump then pumps cold water but does it? In other words is the boiler simply remaining too hot to come back on for several minutes or does it actually become cool without re-igniting?

Sorry about all of the questions but you need to systematically work out what exactly is happening.

 

[Wildeman]

[QUOTE="Are you saying that you need the cylinder stat at 85 and the boiler stat low for CH only to work? If so, then there is a wiring fault.

Has the electrician checked that the expected voltages are present, depending on the status o the programmer and room/cylinder thermostats?

Was the previous valve also a Sunvic Mo-Mo?[/QUOTE]

If the Cylinder Stat is at 80 and the boiler stat low the valve remains in the mid position and I get CH and the water heats as well but the DHW tank never reaches 80 - well not before we are done with the heating.

The electrician has confirmed all voltages are as expected with all status of the programmer, room and Cylinder thermostats. The previous valve was a Sunvic Mid Position spring return valve but Sunvic Technical department confirmed the Mo-Mo is a like for like swap.

 

[Wildeman]

The pictures don't show anything obviously wrong with the layout and at the moment I doubt that the programmer is causing this problem.

If I was there I'd want to look very carefully at the behaviour of the boiler and pump when in CH only mode while monitoring the voltage supplied to both.

Does the pump run and does it definitely keep running after the boiler goes off.
Is the boiler switching off because it is quickly overheating?
You say the pump then pumps cold water but does it? In other words is the boiler simply remaining too hot to come back on for several minutes or does it actually become cool without re-igniting?

Sorry about all of the questions but you need to systematically work out what exactly is happening.

In answer to your questions:

When in CH only position on the valve the pump runs and when the boiler goes out the pump keeps running until the programmer switches off the CH
It would appear that the boiler is switching off due to quickly overheating and I stood by it for 20 mins and it did not appear to relight or try to relight
In answer to your last question this is what I observed this morning:

6am - Programmer switched on the CH and DHW together
The DHW Cylinder was demanding heat and so to was the room stat
The valve was seen to move to the mid position (there is a visual indicator on the side to show what position it is in and this was checked by removing the head which was indeed in the mid position)
The pump started to run and the boiler ignited and the pipework to the pump and from ports A and B on the valve got red hot
The radiators ALL became hot
6:22am - Programmer still switched on CH and DHW but DHW tank stat hits 65 degrees
Room stat still calling for heat due to house being cold due to cold night
Valve starts to move to CH only position - pump stops during the move and boiler goes out
Valve reaches the CH only position (again confirmed by removing the head quickly to check position)
Once valve has reached the CH only position the pump starts and the boiler ignites
After about 40 second the boiler goes out and the pump keeps running
6:35am - Programmer still switched on CH and DHW and DHW tank stat still at 65 degrees
Room stat still calling for heat
Valve still in the CH only position (visual check again)
Pump running but boiler NOT lit and all the pipe work to the pump and from Port A (and the top of Port B pipework) cool to the touch and getting cooler
No heat in the radiators - chrome towel rails cooling down

Remains like this until 6:50am when I remove the valve head and move the valve body to mid position - pump is still running but boiler fires and all pipework and rads get hot.

7am - Move valve manually back to CH only position and refit the head - pump still running - boiler goes out and pipes and rads cool off - pump constantly running.

7:20am - run a bath with a large amount of hot water - DHW cylinder stat calls for heat and so is the room stat - valve moves to mid position - pump is running and continues to run through the valve move
When the valve hits the mid position the boiler fires and all pipework and rads get hot until 7:40am when the DHW cylinder stat is satisfied and the cooling to the rads starts again...............................

As there is no-one in the house all day drawing off hot water I expect when the heating kicks in it will work for a short time until the DHW cylinder reaches temp (will be a short time as no draw off since this morning) and then there will be not heat in the radiators all night unless I turn up the DHW cylinder stat to 80!!!

 

[D_Hailsham]

If the Cylinder Stat is at 80 and the boiler stat low the valve remains in the mid position and I get CH and the water heats as well but the DHW tank never reaches 80 - well not before we are done with the heating.

The electrician has confirmed all voltages are as expected with all status of the programmer, room and Cylinder thermostats. The previous valve was a Sunvic Mid Position spring return valve but Sunvic Technical department confirmed the Mo-Mo is a like for like swap.

So you are "cheating" by setting the valve to mid-position to get the rads heating up. Not quite sure why you turn the boiler stat down as this will mean the rads do not get so hot. Is it because the boiler will otherwise cut out?

You should be getting 240V on the valve's grey and white wires when CH ONLY is called. There should also be 240V on the orange wire.

 

[Wildeman]

If the Cylinder Stat is at 80 and the boiler stat low the valve remains in the mid position and I get CH and the water heats as well but the DHW tank never reaches 80 - well not before we are done with the heating.

The electrician has confirmed all voltages are as expected with all status of the programmer, room and Cylinder thermostats. The previous valve was a Sunvic Mid Position spring return valve but Sunvic Technical department confirmed the Mo-Mo is a like for like swap.

So you are "cheating" by setting the valve to mid-position to get the rads heating up. Not quite sure why you turn the boiler stat down as this will mean the rads do not get so hot. Is it because the boiler will otherwise cut out?

You should be getting 240V on the valve's grey and white wires when CH ONLY is called. There should also be 240V on the orange wire.

Correct in "cheating" using the valve - I tried turning the boiler stat down with the DHW cylinder stat right up to keep both the heating and DHW calling for heat to keep the valve in the mid position with the head on

When CH only is called I do indeed get 240v on the Valve's grey and white wires and it is a constant 240v - there is constant 240v on the orange wire as well

 

[jackthom]

Iv'e a feeling we've already covered this but just to be clear.

Can you confirm.. with the actuator removed and the boiler happily supplying both CH and DHW, what happens when you physically turn the valve body spindle towards the CH Only position.

 

[Wildeman]

Iv'e a feeling we've already covered this but just to be clear.

Can you confirm.. with the actuator removed and the boiler happily supplying both CH and DHW, what happens when you physically turn the valve body spindle towards the CH Only position.

There is a change in the noise of the pump and then the boiler goes out after about a minute and the pipework goes cold eventually - the pump keeps running throughout the whole test

 

[jackthom]

I don't understand how the valve can close off both ports A & B in that way. But if it really is somehow doing that, then personally I would be looking to replace it with something like a Honeywell 4073A.

 

[Wildeman]

I don't understand how the valve can close off both ports A & B in that way. But if it really is somehow doing that, then personally I would be looking to replace it with something like a Honeywell 4073A.

It is not closing off both ports A & B - this has been checked by removing the valve and inspecting which ports are open and it is working as expected. All the 3 valves have been the same so it cannot be that all 3 are faulty

 

[jackthom]

OK one last question. When in CH only mode, the boiler is firing for 40secs or so. How far through the system does the brief burst of hot water circulate. Can you feel it getting past the 3 port valve and onwards in the pipework going towards the radiators?

I should also check that the pump is on the highest speed setting.

 

[D_Hailsham]

The pipework under the floor is 28mm reduced to 10mm close to the radiators where the 10mm tails run through the walls to the rads.

We seem to have eliminated the valve as a cause so the only thing left is circulation.

The maximum boiler output is 17.58 kW (50k BTU) but it can be reduced to a minimum of 14.65 kW. When both HW and CH are running the rads and cylinder can handle the boiler output; but when only the CH is on the rads cannot absorb the output, so the system overheats and the boiler cuts out.

Use the data in the Stelrad Catalogue (page 44) to calculate the output of your rads.


PS the temperature 20 degree difference you mention is degrees F. This is important as heating engineers now work in degrees C and 20C is 36F!. Modern condensing boilers are designed to work with a difference of 20C, but not your boiler where an 11C difference is expected.

 

[Wildeman]

OK one last question. When in CH only mode, the boiler is firing for 40secs or so. How far through the system does the brief burst of hot water circulate. Can you feel it getting past the 3 port valve and onwards in the pipework going towards the radiators?

I should also check that the pump is on the highest speed setting.

The hot water gets past the valve and down the pipe that goes towards the radiators. The pump is on the middle setting.