Header overflow - should be so simple.

[Terry Godber]

Is there a branch between the ballofix and the ball valve?
If so, where does it go to?

Hi Ian,
Why exactly do you ask? I am hoping you have a point here, in fact there is a mcw branch which tees off between the ballofix and the float.
It tees off between and then runs over at high level before it then drops to serve a Redring Powerstream electric shower. The connection has been in place like this for a decade without issues and the Redring only has a cw supply.

 

[Terry Godber]

No transfer across the pump so rule that out.

Thought not...

 

[Ian10261]

Hi Ian,
Why exactly do you ask? I am hoping you have a point here, in fact there is a mcw branch which tees off between the ballofix and the float.
It tees off between and then runs over at high level before it then drops to serve a Redring Powerstream electric shower. The connection has been in place like this for a decade without issues and the Redring only has a cw supply.

If, as you say the problem goes away when you turn off the ballofix then it follows that mains cold water entering the gravity system is the cause of the problem.
It also follows that the problem lies downstream of the ballofix. If the ball valve is not letting by then its obviously going somewhere else.
I was wondering if the feed to the sealed system filling loop was branched off after the ballofix, the filling loop was letting by, the gauge had stuck and the cylinder coil had failed. A long shot i know but stranger things have happened and 30 years is a good age for a cylinder. I've known them to fail well before that age.
Problems like this can be very hard to pin down but mains water is definately getting into the gravity fed side somehow and then backfeeding into the cws. Have a good look at that branch pipe again and see if there is anything else it feeds into.
Hope this helps.
Ian

 

[Terry Godber]

Hi Ian,
Testing a potential solution... years earlier the original feed to the ensuite was gravity via a line teed off the side of the 18mm cw gravity feed at 1st ceiling level.
Later the Redring was introduced [at the time the pump was not in place] and no surprise the flow was inadequate so a separate mains feed was then introduced.
At this stage the gravity feed and the mains cw feed were linked via a ballofix isolator before the shower unit, thinking one day I will add a pump.
Problem may well prove to be that because the ballofix was first to isolate the gravity feed the mains pressure connection to the ballofix was then reverse flow. Over time it has been OK and unused [closed]. I did operate it a little while back [just to stop it seizing I thought] but now when I come to it today, it leaks at the slotted screw but only when its turned again.
Right now its removed and relevant connections are terminal capped leaving the mcw feeding the shower and removing the interface.
Hopefully, I will let you know that my issue has been fixed in a couple of days. Any way thanks for your question which may well have rattled the right chain.....

 

[Ric2013]

If I understand you:

You have a working spring loaded one way valve (a proper check valve, airtight, not a flap valve that is only ish) on the cold distributing pipe, so we can rule out problems with mixer taps backfeeding up the cold distributing pipe.

You have a similar valve on the cold feed to DHW cylinder, then that rules out split coil and mixer taps passing water back up the cold feed.

The water can now only get into the cylinder from the top: the vent and the fill valve. Since the vent is only allowing a few drops of water through, we can assume that is normal expansion of water and not a punctured coil or mixer issue causing backfeeding through the DHW cylinder and vent pipe.

At this point, either you have a very leaky roof, or the water is coming in through the ballcock, impossible as it may seem.

Do I understand correctly, Terry?

If so, at this point, use a 15mm blanking cap on the tap connector that normally goes onto the ballcock and, if the level of the water does not rise overnight, I'm right, as by capping the ballcock, you aren't affecting anything else. If the level still rises, I'm missing something.

Final thought: is the overflow shared with something else and the cistern is filling through the overflow?

 

[Ric2013]

Hang on... is there a lid on the tank or could a bird be perching on the float arm?

 

[Ric2013]

I was wondering if the feed to the sealed system filling loop was branched off after the ballofix, the filling loop was letting by, the gauge had stuck and the cylinder coil had failed.

Ian. Agree with your thinking, but, if the one-way valves are working correctly and are proper spring-loaded check valves then I must respectfully disagree because the only way the water added to the cylinder could backfeed the cistern is through the open vent, and the OP tells us he has a cup under the vent and can prove this isn't happening.

 

[Ian10261]

Hi Ian,
Testing a potential solution... years earlier the original feed to the ensuite was gravity via a line teed off the side of the 18mm cw gravity feed at 1st ceiling level.
Later the Redring was introduced [at the time the pump was not in place] and no surprise the flow was inadequate so a separate mains feed was then introduced.
At this stage the gravity feed and the mains cw feed were linked via a ballofix isolator before the shower unit, thinking one day I will add a pump.
Problem may well prove to be that because the ballofix was first to isolate the gravity feed the mains pressure connection to the ballofix was then reverse flow. Over time it has been OK and unused [closed]. I did operate it a little while back [just to stop it seizing I thought] but now when I come to it today, it leaks at the slotted screw but only when its turned again.
Right now its removed and relevant connections are terminal capped leaving the mcw feeding the shower and removing the interface.
Hopefully, I will let you know that my issue has been fixed in a couple of days. Any way thanks for your question which may well have rattled the right chain...

Ian. Agree with your thinking, but, if the one-way valves are working correctly and are proper spring-loaded check valves then I must respectfully disagree because the only way the water added to the cylinder could backfeed the cistern is through the open vent, and the OP tells us he has a cup under the vent and can prove this isn't happening.

Ian. Agree with your thinking, but, if the one-way valves are working correctly and are proper spring-loaded check valves then I must respectfully disagree because the only way the water added to the cylinder could backfeed the cistern is through the open vent, and the OP tells us he has a cup under the vent and can prove this isn't happening.

Ric, i know exactly what you're saying and that was rattling round in my head as i wrote my reply to Terry but we don't know for sure what kind of check valves are fitted. As you'll know some have quite a high opening pressure and if fitted next to the cws then you'd have zero or very little flow to begin with. On that basis i was assuming that he'd fitted the old swing check valves that we used on old CH systems to stop gravity circulation through the rads when in HW mode. As you said they don't completely seal off especially if they're installed horizontally which would most certainly allow any mains pressure water to get past. The way i see it is this; when he turns off a ballofix on a mains pipe the problem stops. Having replaced the ball valve 4 or 5 times we can rule that out, can't see it filling through the overflow as there's no F&E tank, next to nowt coming from the vent pipe so short of a hole in the roof it just leaves the outlets. Difficult one this as nothing adds up and its never easy solving problems via a keyboard. I'd love to be able to go sort it but i'm recovering from a broken back which is half the reason i'm on here, gives me something to do to relieve the boredom.

 

[Last Plumber]

I think, having read through this thread, you need to get a Plumber/Heating Engineer in to look it over.

There are a few things that don't sound right. It may just be the terminology that you are using Terry but for safety's sake, I would advise you get someone in.

 

[Ric2013]

As you'll know some have quite a high opening pressure and if fitted next to the cws then you'd have zero or very little flow to begin with.

That was what raised my concern that he may have fitted swing valves and not proper check valves that would actually prevent backflow, rather than just slow it down a little. In my experience, single check valves aren't much use when the taps served by the check valve are less than two floors below the cistern, so a friendly merchant may well have supplied swing valves instead.

At this stage the gravity feed and the mains cw feed were linked via a ballofix isolator before the shower unit, thinking one day I will add a pump.
Problem may well prove to be that because the ballofix was first to isolate the gravity feed the mains pressure connection to the ballofix was then reverse flow. Over time it has been OK and unused [closed]

Thanks for highlighting that again, Ian. This is a matter of concern as to what dead legs may be present and also how the mains is protected from contamination. It may also be the cause of the problem, as a directional isolation valve may well not seal properly if the flow direction is reversed. I had originally read this section as meaning something completely different from what the OP has actually written, so I'm glad you've quoted it, thus forcing me to read it again.
Now I'm inclined to agree with Harvest: unless the OP can supply a diagram of the system, it's now sounding too weird to be solved by keyboard.