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

[andywilde16]

Hello,
I am after some assistance with the issue I have with my Open Vented, Fully pumped Central Heating system.

I have a Glow Worm Ultimate 60BF boiler, Sunvic MoMo 3 Port Mid-Position Valve, Sunvic Digi Stat, Sunvic Programmer, TRV's fitted to all but 2 rads, Honeywell Tank Stat and a Wilo Gold RS pump

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!!

I have had an electrician rewire all the components and the box in the airing cupboard, the pump has been replaced recently as to has the cylinder stat and mid position valve. The programmer too has been replaced and the electrician confirmed all the DIP switches are set right and it is set to fully pumped.

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.

Could the issue be flow through the boiler causing the issue when the valve is in the heating only position as the boiler manual states "the flow through the boiler must not be allowed to fall such that there is a temp difference greater than 20 degrees between the flow and return"

If so how can this be resolved - balancing the radiators?

Any assistance would be greatly appreciated as I have ruled out the electrics, components such as pump and valve and the pipework appears ok so the only thing left is the boiler.

Thanks

 

[gmartine]

Re: No Central Heating only - fine on HW and CH or HW only Read more: http://www.diy

Boiler temp stat down?

It can only be the boiler thermostat or room stat that is turning the boiler off prematurely. Is the room stat functioning properly and is it set up correctly?

 

[andywilde16]

Re: No Central Heating only - fine on HW and CH or HW only Read more: http://www.diy

The room stat has been checked and when it calls for heat and the DHW is up to temp the valve moves to the CH only position and the pump runs, the boiler lights and then goes out shortly afterwards.

If the boiler stat was at fault would it mean the boiler would not work on DHW and CH together?

What is weird is if the valve is in the CH only position and the head is removed - once the cam on the valve body is moved slightly towards the mid position the boiler fires instantly and the pipe to the pump gets red hot - move it back to the CH only position and the boiler goes out and the water runs cool to cold eventually!! This is what leads me to believe it is flow or temp differentials at or through the b

 

[gmartine]

Re: No Central Heating only - fine on HW and CH or HW only Read more: http://www.diy

The boiler stat doesn't differentiate between settings, it should be set on max though.

 

[andywilde16]

Re: No Central Heating only - fine on HW and CH or HW only Read more: http://www.diy

The boiler stat doesn't differentiate between settings, it should be set on max though.

I turned the boiler stat up to max last night but still no difference no CH only

 

[gmartine]

Time to get someone in.

28mm to 10mm tails probably doesn't help, has the system worked properly before you DIY'ed the upgrade?

 

[andywilde16]

Time to get someone in.

28mm to 10mm tails probably doesn't help, has the system worked properly before you DIY'ed the upgrade?

It is hard to say for sure ever since we moved in the DHW Cylinder stat has been set on 80 and the boiler state midway - it was only really noticed when I turned the DHW Cylinder stat down from 80 due to tap and shower pump demands!!

I haven't DIY'ed any upgrade just replaced the pump and valve with like for like replacements. I have pictures if it would help of the piping and pump/valve arrangement