No Hot Water Puzzle???

Correction - water from hot water taps is not as warm as 20 celsius. More like 12.

Weird. Coil sludged up maybe resulting in poor heat transfer and low flow through coil? Do you have very hard water? Could your tank be full of scale? Did this come on suddenly or has it been a gradual reduction in performance? What happens if you turn CH off and force all flow through coil?

Tim

Check temp of water at 2 port valve for heating coil by holding pipe. Check 2 port valve for heating coil is fully opening by removing motorised head and working manually. See how hot DHW gets when valve is manually opened. Should warm up in half an hour?

I had a 2 port spring return valve fail because the head had separated from the shaft. You could turn the pivot and nothing happened. This will show up when he checks the pipes either side are hot.

Should the radiators be hot with the valve manually overidden to HW?

Might be just conduction along the pipe work. The pipes coming out of the thermal store here get a decidedly warm some distance from the store.

So check the valve is actually doing what you think it is. ie when set for HW only the rads don't get hot. Maybe take the head off as others have suggested.

Do all the rads get hot or only those upstairs/above the boiler. Pump might have failed.

Why not? He has "2-port motorized valves" i.e. one for each circuit.

MBQ

HW is normally the spring return position. The manual override in all mine is the mid-point position, with both HW and heating on (which makes sense as it's mainly there for filling and draining the system).

Yes - do check the temperature at the cylinder end of the flow/ return pipes.

Bit worrying though that flow rate is good and ok one day but not next.

Brian

off-the-wall:- Continuous leak from hot water side so tank never warms up? "Short circuit" between hot and cold somewhere so that hot just draws from cold?

Er . . it's an S-Plan system with two 2-port valves, not one 3-port mid-position valve.