Water cool in the morning

[jakefouro]

Hi all, I recently installed a stove with a back boiler and installed a dual coil cylinder which is now heated by the existing pressurized gas boiler and the open vented back boiler. I have noticed that even though both heat sources are heating the water at night, the water is cool in the mornings - so cool that I can not have a shower.
The cylinder appear to be losing heat during the night for some reason. It is a new factory insulated boiler.
Any ideas as to what the problem is.

 

[twgas]

I would suspect a leak on the hot tap supplies

 

[jakefouro]

That had crossed my mind, Mick, but no obvious leaks!

 

[namsag]

Do any of your hot water pipes to taps go under concrete floor or suspended floors down stairs

 

[jakefouro]

Actually the supply to all taps from the cylinder is routed under the concrete floor. What I could do to rule out an underground leak would be to shut off the stop cock coming from the cylinder. Will try this and report back during the week. Ta.

 

[namsag]

Try looking for damp or a hot patch,

 

[Jonnie]

The ballvalve in the hot water header tank in the loft would be constantly dripping if there is a leak

 

[jakefouro]

Cant seem to locate any wet or hot spots under the carpet or tiles. No drip from the loft cold water tank. Water hot tonight so I have closed the gate valves on the flow and return pipes between the boiler and the cylinder. Should be warm/hot in the morning - if not the puzzle remains!.

 

[Anybody]

If there was a fault/ design error and a pump was still running for a long time after the solid fuel fire had died down then hot water could be circulated back to the stove where it could lose its heat in between.

Making sure a pump doesn't run in such a way would be a good plan and insulating the pipes would be another.

 

[jakefouro]

Pump from solid fuel stops circulating once stove temp drops below 45deg. Last night, closed off gate valves on flow and return from gas boiler to cylinder and lots of hot water available this morning. Because of problems with blockages,leaks in the CH undefloor pipes to the rads and cylinder in the past, the pipes were relocated to the attic. So, the hot water pipes exit the cylinder, travel directly up to the attic and then down to the boiler.
Is it possible that the heat is leaking from the cylinder and circulting back to the gas boiler during the night, because the hot water can rise?

 

[Anybody]

Pump from solid fuel stops circulating once stove temp drops below 45deg.

When the stove temp is 46ºC it will still be circulating and taking your hot water down to that temperature. Could you alter this to say 60 and see how it goes ?

Is it possible that the heat is leaking from the cylinder and circuiting back to the gas boiler during the night, because the hot water can rise?

Highly likely. Although I suspect it is whats known as one pipe circulation basically the single highest pipe acts as a heat emitter on its own by the convection currents within the pipe. If this is the case fitting a dip pipe to the top cylinder connection and sorting out a vent at that point will cure it.
By a dip pipe I mean take the pipe from the top cylinder connection and send it vertically downwards for 200mm and then back up toward the loft. Before the pipe dips down you will have a high spot where air will collect. Fit a manual air vent here.

Theres two things to go on and the answer could lie with either or both. Perhaps another phenomenon but at least you have something to go on.

 

[jakefouro]

Thanks anybody - two things to work on. Will obviously try increasing the pipe stat temp first. I do feel though that the convection theory may be the culprit.