Water being blown through tun dish

[hi1]

Hi, the situation is this. Ballon French water heater a cross between immersion tank and pressurised system as I understand it. There is a safety module under the tank which has prv, tun dish and cold inlet connected. the dish has water in it which according to French manufacturer is o.k in normal operation. The tun dish drains along abs pipe into a boxed in area where the bathroom sink and shower also drain to. When the basin plug is pulled gurgling and back flow of water from the tun dish happens, so presumably sink and tun dish drain meet somewhere and air is being forced back up pipe causing the noise and overflow. to prevent this would an inline anti syphon valve sort the problem or a mini air admittance valve in the tun dish pipe be a better bet. the owners are 80 plus haven't a clue about plumbing but have invited a French plumber around to empty their wallet, this I would like to prevent if possible. Thanks for reading.

 

[KenGMac]

hi1, good evening.

OK I admit i do not have a skubbie as to the "system" you describe?

But??

Have you considered a blockage in the drain down stream of the basin??

Just a consideration?

Ken.

 

[hi1]

Hi, thanks for your reply but its been on going for a year, doesn't happen every time only when tun dish has sufficient water in it, and basin drains away fine. I thought would an air admittance valve allow the air being pushed up the tun dish pipe by the basin water flowing to vent away or would an anti syphon valve allow air out?

 

[dilalio]

It's hard to picture without a diagram or photos but it all depends how and where each component is connected to the drain.

If the shower is furthest downstream and doesn't back up, which it should, having the lowest flood level, if there were a downstream blockage, then the connection between basin and tundish pipework needs to be surveyed.
The tundish (unless a specialist design) is an air gap and is not trapped so there needs to be a trap in the run somewhere.
An AAV is only of any use when traps are being pulled... Whereas here, it sounds like the tundish and its associated pipework is acting as a vent.

 

[ianmcd]

The correct name for this water heater is "chauffe eau ballon ou instantané" you might be able to find installation instructions online, the Tundish is merely there so that any water being discharged from the safety valve is visable and not constantly running and the customer is not aware, under normal operating conditions there should never be any water in the tundish, the problem is the drain is backing up, either wrongly sized pipe or a partial blockage somewhere, if it is possible disconnect the tundish pipe from the drain and divert it to outside and terminate at ground level, as said it is an emergency relief pipe and shouldn't have water in it unless the safety valve has operated so dont normally get installed into a drain pipe

 

[hi1]

Thanks for your replies, appreciated

 

[Nozzle]

There should be no water in the tundish and any that is in there should be able to drain all the way outside to a low level so any hot (potentially V.HOT) water gashing out doesn't scald anyone.

If there water that is there, ended up there because the drain is backed up, it needs unblocking. If it's also dripping then the PRV is unseated, perhaps because of loss of expansion room.

Nozzle

 

[hi1]

hi having done some more research the consensus is that these things do allow water by whenever the tank is being heated, I know they shouldn't. The French seem to be catching up abit in that there is now an option to fit an expansion vessel to the safety assembly, pics to follow hopefully. French regs also state that the overflow has to be connected to the sewerage system but doesn't say whether this has to be directly or can be via another connection.

They even had to the nerve to try and make French plumbing as an e.u standard.

 

[Nozzle]

Then it makes sense for the tundish to have a vapour trap if it is connected to the sewer.

Your description of the PRV makes it sound more like a regulator with a constant bleed. Or something just as weird

Nozzle