cwsc keeps overflowing

[wigz]

hi guys i work in a building with 3 floors,
ground
first = cylinder
second = cwsc

the cylinder feeds a sink and a bath on the first floor and a sink and bath on second floor, the problem is every month or a couple of months the cwsc fills up and floods 3 floors in a residential home, dozens of plumbers (contractors) and gas engineers have been to the job doing various things but have never stopped the problem,

on top of the cylinder is a pump pumping water up to the floor above feeding the sink and bath it also pumps to the same floor also sink and a bath, i have noticed one thing that i keep trying to explain to the workers, on all the hot feeds are loops to create instant hot water, but i thought with a loop you tee off the hot water pipe say under the sink and back into the hot water pipe at the cylinder creating a pumped loop,therfore erasing the dog leg of cold build up,

but what some plumber has done instead of teeing back into the hot water near the cylinder, the plumber has actually tee into the cold feed from the cwsc, so basically making the the whole system a pumped syem.
also on the cold feed from the cwsc is a non return valve which shouldnt be there, so im thinking the water is blowing past the non return valve and back into the cwsc?, they obviously no something is up to put a non return valve on that pipe. i know its gonna be hard for you guys to picture it but all help is gratefull thanks .ps i work there a couple of hours as a cleaner helping out but as i have done 5 year apprentice and plumbing diploma i am somewhat curious.

ps this problem is on going for 6 years, but has got worse as people are using the baths and sinks a lot less,the water temps are tested twice a week for safety so think that rules out over heating, and i dont think that water is entering cwsc via the open vent

 

[justlead1]

Hi, On baths and basins etc, are there mixer taps?

 

[wigz]

na theres no mixers, but under the sinks are thermostatic mixer valves to regulate the hot

 

[david williams]

disconect hot service where it conects into the cold water down sevice and re route it back to hot water cylinder,reconect to cylinder 1/4 of way down from top of cylinder with essex flange,remove non return valve

 

[wigz]

so will that not still create the same problem? because the water will still pumped entering the cylinder?

 

[justlead1]

Hi I would investigate the mixing valves first, they may be mains feed? Good luck

 

[wigz]

what if the mixing valves are main fed??

 

[justlead1]

Hi. I take it that the cwsc. overflows rather than floods the property? The circulation mentioned on the secondary return would not effect the water level in the cistern, other than the expansion of water when heated. Mains pressure on cold supply is likely to be 10 fold that of the hot water system, as a result the mixing valves may well be letting by and filling the system via the hot distribution pipe under certain conditions. Good Luck

 

[stevetheplumber]

what if the mixing valves are main fed??

they will back feed the hot water systen

 

[REDSAW]

check the warning pipe size and increase its dia' first as any overfilling should flow out of the building to start with, check its not blocked either.
it seems to me its going up the exp pipe.
once any over flow is directed outside the building, call round when over flowing and it will be more apparet on research whats happening.

 

[wigz]

hi the mixer valves under the sinks are mains fed, but on the main pipe before the mixer valves are regulaters to slow down the flow, but also the hot going into other side of the mixer valves is pumped, so do you think mains could push its way against pumped hot?.

 

[justlead1]

Hi. Yes mains pressure is the likely cause of the problem. Is it possible to run the cold via the cwsc on gravity?

 

[Alanka]

Two immediate thoughts:

1) The overflow pipe fitted to the cwc should prevent any overflowing of the cistern under fault conditions. Any overfilling should flow safely to outside via the overflow/warning pipe and should be clearly visible if it happens. So something is wrong with the overflow arrangements!

2) The outlet pipe at the bottom of a cw cistern also acts as an expansion pipe to allow heated expanded water from the hw cylinder to flow upwards into the cw cistern. (It's a common fallacy to think that this happens via the hwc vent pipe - which is for emergency overheating or boiling only.) So fitting a non-return valve in this pipe is a no-no, and will cause the expanded water to flow up the vent pipe instead, which is not what it is designed for.

 

[wigz]

the reason why the the cwsc overfloes is because the connection on the cylinder is 35 mm, so expansion is 35mm coming up to cwsc and the cold feed from the cwsc to the cylinder is 35 mm also, incoming main is 15 to cwsc and warning pipe is 22mm, 22mm is fine compared to 15 mm main coming say if ball valve fails, as i said water is coming up the cold feed i think hence why they fitted a non return valve to it,

also with the mixer valves under the sink if mains pressure was forcing the hot back to the cylinder, then when i turn the hot tap on i will be getting cold at least for a couple of seconds but the water is instantly hot also feeling the valves underneath there is hot going all the way to the valve no cold back up. would that suggest the valve isnt forcing the hot back to the cylinder with mains pressure ?

 

[justlead1]

Hi. The expansion you mention does not relate to the pipe size and the non return valve should not be here. If say the cylinder is 100 gallon on heating through 60 degrees the volume of expansion may be 3 gallon max. I would be looking for a cross connection of some kind ( the mixers or temporary rubber shower hoses fitted to bath taps, check the whole system) Also check if the cylinder is indirect. Unlikley but coils within the cylinder have been known to fail. My way forward would be to isolate mains to mixers (stopcock /ballafix valve) drop temp of stored water (discuse and confirm with management) Monitor performance over say a week. Remember your not a magician, some time clients have to spend a lot of money to get things right.

 

[wigz]

thanks for the advice.