vented direct hot water cylinder expansion problems

[alpina1970]

thanks gasguru the non return valve is fitted just after gate valve on cws and not near cylinder, cws is 150 gallon as it is in a small hotel, no other mixing valves apart from 3 monobloc mixers with washers replaced, the cylinder is fed from a single 28mm copper feed straight to cylinder, hot water draw off is 22mm with tee around 8 inches from top of cylinder rising up via roof and with expansion pipe bend over roof tiles about 3 ft . ...another way to look at this from top of water level in cws to expansion pipe going out through roof is approx 4/5 ft the immersion heater stat has also been changed over and temp sitting at 50c, so no possible that its boiling over, only when gate valve feed to cylinder is shut down that the water stops via expansion.

 

[alpina1970]

sorry forgot to add that the only reason for the swing type non return valve was that there was the backflow of water coming back into cws and making the water level rise that far it was coming out overflow pipe, hence that the problem has shifted to expansion pipe.

 

[mogget]

There is only one possible thing: you have some other higher pressure source feeding into the hot water distribution / cold feed somewhere.

Pinholed cylinder coil / thermal store / mixers passing etc.

 

[Gasguru]

Take the swing check valve off....it must not be there. When the cylinder is heated the cylinder water must be allowed to expand back up the feed pipe to the cistern.

Are you saying water emerges from the vent pipe even with all outlets OFF?

If you isolate the cold feed to all the outlet does the backflow stop?

 

[stardanny]

3 monobloc mixers with washers replaced

Turn off cold water supply to these mixers, it may be pinhole leak between both hot and cold supply inside body.

only when gate valve feed to cylinder is shut down that the water stops via expansion.

Exactly, that what confusing me. It rule out anything that connected to hot supply from main.

There is one thing come to my mind that can cause this but I'll have to look in my paperwork, impossible but....

Daniel.

 

[mogget]

only when gate valve feed to cylinder is shut down that the water stops via expansion.

Sorry, misread that - read it as feed to cistern

 

[Gasguru]

As previously mentioned if this is an indirect cylinder AND the coil has perforated AND the primary F&E cistern is above the secondary vent outlet then that could be a source of the problem too.

And mentioned by stardanny a mixer could be faulty allowing cold mains to flow to hot even even off.

 

[stardanny]

A photo of cylinder and pipework would be good.

Daniel.

 

[alpina1970]

gasguru water shouldnt be expanding up via feed pipe as this would be seen under contamination ofwater this is only reason for non return being fitted, might add that this was the original problem that cws was filling up, it will be removed when problem has been sourced, there is no restriction on hot water draw off/expansion from cylinder, cws ballcock does not run when the the water is coming out expansion, i know that there can only be a few if any possible explanations for this but we will have to 200% check to make sure that the cws is only feeding cylinder without any possibilty without any other branch offs or anything feeding into it.

 

[alpina1970]

its a direct cylinder so no coil fitted

 

[Gasguru]

Of course the water expands back up the feed pipe...where else is it going to go when the cylinder is heated. The volume of expansion water when the cylinder is heated is minimal so not a problem. By not allowing the expansion back up through the feed you are just adding to the problem.

You still haven't answered the questions....does water emerge from the vent pipe when the outlets are off or just when water is drawn off?

 

[alpina1970]

only emerges when no water is drawn but can take up to 20 mins , expansion of water is usualy 10% we have allowed for this and lowerd the level of ballcock in cws and it still was rising to overflow

 

[Gasguru]

Thermal expansion is nothing like 10%, more like a couple of %

Isolate the cold feed to all outlets....the problem will go away, proving there is a problem with let by on a mixer outlet.

 

[alpina1970]

thanks gasguru will let you know results on tuesday

 

[alpina1970]

Thanks guys problem sorted. .faulty shower mixer valve ...