No Hot Water Puzzle???

[steve wells]

Standard indirect vented hot water & heating system, Potterton/ glowworm boiler with 2-port motorised valves to rads & Hot Water cyclinder. Fully pumped (1 pump serves both circuits)

Hi I've only got lukewarm water coming from hot water taps & shower. (say

20 degrees Celsius). The flow rate is normal. Boiler on for 1 hour plus. Normally 30 mins sufficient. Radiators hot. Hot water motorised valve on (manual overide) Cylinder coil flow & return pipes both hot. Cylinder hot water draw off pipe coming out of cylinder top just doesnt get hot, barely warm after even hour.

Surely, If there was air lock in cylinder coil then both coil flow pipes wouldnt be hot. If air lock in the hot water supply pipework including cylinder then flow rate from taps wouldnt be normal. If limescale around cylinder coil, it worked fine one day, then not the next. Surely limescale buildup & effects would be noticed gradually. If sludge in coil then why coil flow & return both hot.

Going to crawl up into loft tonight but cant at the moment think anything up there would cause this like stuck ball valves.

Are my assumptions wrong or what am I missing?

Steve

[steve wells]

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

[Tim]

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

[harryagain]

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?

[dennis]

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.

[Dave Liquorice]

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.

[Man at B&Q]

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

MBQ

[Andrew Gabriel]

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.

[Brian Gaff]

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

Brian

[Geo]

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?

[Roger Mills]

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