Hot water 'back flowing' to header tank

[Darren Woodall]

Hi all,

Sure this has been answered many times but can't quite see previous post which covers this. I'm not a plumber which will likely become obvious!

So, currently suffering from constant run-off from F&E overflow into garden - moderate flow, like a tap is on!

The F&E tank is filling up due to back flow from the gravity pipe out of the tank (aka reverse flow). Just to confirm the tank is not filling up via the mains feed/ball valve and not through expansion via the vent pipe. It's back flowing with warm/hot water back up the outlet.

I confirmed this by tying off the ball valve and emptying the tank, I can see the water returning into the tank once emptied from the bottom of the inside of the tank.

It does this whether or not the boiler is on or off.

I'm of a mind to think it's either a compromised coil in the hot water cylinder or a problem with the mixer shower. I'm going to isolate the mixer tomorrow just to see if the problem does stop.

If it's not the mixer I'm of a mind to replace the cylinder but am I on the right track or barking up the wrong tree! Is there anything else which could cause this? I don't want to replace the cylinder uneccessarily.

Many thanks in advance

Dar

 

[sammathias]

If it was the shower or tap mixer it would only be backflowing into your hot water header tank (big one). Sounds like the coil in your cylinder has failed as you said.

 

[Harvest Fields]

Are the feed pipe and the expansion pipes separate or do they link together?

 

[Last Plumber]

If the cold water storage (CWS) tank water level is higher than the F&E tank water level then it is most likely your Cylinder coil, (presuming it is an indirect, copper, tank fed cylinder here)!

If you want to prove it you could shut the cold feed valve from the CWS tank to the cylinder and once the level in the vent pipe has dropped (open a hot tap) it should stop, as long as the valve does shut that is. If not or if there is no valve, it will need to be drained.

 

[Darren Woodall]

Are the feed pipe and the expansion pipes separate or do they link together?

Hi. Separate.

 

[Darren Woodall]

If the cold water storage (CWS) tank water level is higher than the F&E tank water level then it is most likely your Cylinder coil, (presuming it is an indirect, copper, tank fed cylinder here)!

If you want to prove it you could shut the cold feed valve from the CWS tank to the cylinder and once the level in the vent pipe has dropped (open a hot tap) it should stop, as long as the valve does shut that is. If not or if there is no valve, it will need to be drained.

Yes the CWS is higher than the F&E and yes it's indirect vented copper tank fed I'm almost certain now it's the HWC coil. Thanks

 

[Darren Woodall]

If it was the shower or tap mixer it would only be backflowing into your hot water header tank (big one). Sounds like the coil in your cylinder has failed as you said.

Thanks for that, saved me a job. Going with the bad HWC coil

 

[townfanjon]

In my experience they are rare they split , or I may just have been lucky . If I suspect one , I rig up my pressure tester and just test the coil.
If you know a local plumber with a preessure tester it maybe worth a punt.

 

[Ric2013]

You could also tie up the ballcock on your CWSC and see if the F&E continues to overflow until the CWSC has drained to the same level as the overflow, at which point the levels will be the same.

You could even throw some food colouring into the CWSC and see if the colour transfers into the F&E water. No prizes for guessing that I was into DIY long before I trained as a plumber

 

[sammathias]

In my experience they are rare they split , or I may just have been lucky . If I suspect one , I rig up my pressure tester and just test the coil.
If you know a local plumber with a preessure tester it maybe worth a punt.

It is rare, I've only ever had 2 coils fail. Good way to test if the coil had failed, also rics idea. Op did say it was overflowing like a trickling tap so I suspect it's quite a big failure.

 

[PhoenixServices]

I find it fairly common but only ever worked in hard water areas. Oxfordshire and east Devon.

 

[chris watkins]

Note to OP - under Building Regulations Part G (& L) you are required to show that you are competent to cary out this work, you do this by completing a Part G course.
People think just applies to un-vented but it is vented how water storage as well.

 

[Ric2013]

Good isn't it, Chris? NVQ2 has an assessment in which you show you are able to replace a vented cylinder, but then you still aren't qualified to do it. That said, do it right and any action by the authorities is extremely unlikely IMO.

 

[chris watkins]

I think the NVQ2 assessments just show you have the pipework skills not the technical know how Ric but your right no plumbing police out there, only problems are likely to occur if he comes to sell & even then you just buy indemnity.
What a shameful profession we are in.
You should have seen the un-vented I attended yesterday & the wiring

 

[Ric2013]

And even then if it's a like for like replacement...

The neighbour removed the slates from her entire roof, replaced with concrete tiles, and sold the house a few years later. Looks like the subject didn't even come up for query.