Are you quite sure the timeclock is not set for gravity instead of pumped?
Checked and it is set to Pumped
Are you quite sure the timeclock is not set for gravity instead of pumped?
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.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!!
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.
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?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?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.
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.
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.
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.
We seem to have eliminated the valve as a cause so the only thing left is circulation.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.
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.
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