heating not reaching maximum temp

[ianromry]

I have 23 year old potterton suprima 60 with a danfoss flowshare 2 diverting valve and new programmer. I am experiencing short boiler operation of a minute or so before shutting down and then starting up again ( hunting?) Boiler thermostat maximum also room stat maximum but rads only getting warm Any ideas please ? I suspect boiler high limit stat

 

[SimonG]

A circulation by the sound of it, is the pump running?

 

[snowhead]

Is that a new replacement like for like Programmer or did it need wiring alterations ?
Quite possible the New programmer is wired wrong and there's no feed to the pump

 

[ianromry]

I have 23 year old potterton suprima 60 with a danfoss flowshare 2 diverting valve and new programmer. I am experiencing short boiler operation of a minute or so before shutting down and then starting up again ( hunting?) Boiler thermostat maximum also room stat maximum but rads only getting warm Any ideas please ? I suspect boiler high limit stat

Is that a new replacement like for like Programmer or did it need wiring alterations ?
Quite possible the New programmer is wired wrong and there's no feed to the pump

new programmer straight into place no rewiring, pump running normally

 

[ianromry]

new member and not sure if my reply is posted , so ......
new programmer straight into place no rewiring pump running normally

 

[fronty]

I wonder if you've got a blockage somewhere, you could try opening your lockshield valves and see if that improves things, also put the pump onto it's fastest setting if you can.

 

[ianromry]

I wonder if you've got a blockage somewhere, you could try opening your lockshield valves and see if that improves things, also put the pump onto it's fastest setting if you can.

Thanks, will try your suggestion although all rads are same temperature

 

[ianromry]

Pump turned up to max , all lockshields opened, unfortunately no change and temp of all rads the same and pump still runs for about 1 to 2 minutes before shut down and then almost immeadiately re starts and boiler then fires and runs for about 1 minute before shutting off, then ad finitum all day
I am going to renew thermistor and the boiler temperature stat to see if it is a sensing problem

 

[John.g]

Is the pump shutting down because the boiler is cycling every minute or two then shutting down and telling the pump to overrun for a minute or so, then when boiler flow temp falls sufficiently just repeating the process. Can you see what the flow temperature is doing while firing for a minute or so?.

 

[ianromry]

Thankyou for reply, boiler flow temp gets hot ( touch hot but not anything like too hot to touch) then shuts down after a minute . Yes I notice that flow equals return temp before starting up again which is why I thought one or other temp sensors may be at fault and I am awaiting 2no new sensors to substitute but thermistor seems to be in right Ohm range when tested, I am in the process of substituting the boiler temp control to cover all bases Up till now system has worked well and has only had one control board replaced so may be my problem

 

[John.g]

Does it run continuously on HW only

 

[ianromry]

Does it run continuously on HW only

yes, hw is hot to flow temp but not to reqd cylinder temp

 

[John.g]

Not sure what that means, if its firing and its a modulating boiler then it should still output~ 5 or 6 kw which should still heat up the cylinder, it its non modulating then that might only be a pilot flame or something.

 

[ianromry]

Thankyou all for the help and advice , just to clear an outstanding thread, my boiler is fully modulating(I think?)
But after research into the boiler thermostat I think I have found the cause of low heat with continual on/off of boiler. On inspection of the PCB/control board it appeared that the control potentiometer had a dry joint to the board and after a little soldering of the joints and reassembly all seems to be well with boiler and controls working as required with no "hunting" So, fingers crossed all will be well? thanks once again for your help