Very slow movement on water meter but no leak found

[Chris80]

Hello

I am hoping for some advice please. I have recently noticed that my stop tap under the kitchen sink is really tight, so to check we can isolate the supply in an emergency I turned off the stop tap in the road - all OK. However, when turning it back on I noticed the 0.0001 dial is turning very slowly (so much so I reckon many wouldnt have noticed it). I have therefore managed to turn the stop tap under sink off (using a spanner and a lot of force) to fully isolate the internal water supply, there was then no movement on the meter so it seemed small internal leak. I have since done all of the following and the meter i still turning ever so slightly:-

• Replaced kitchen tap valves (as the tap was dripping)
• Changed old toilet filler and flush (as the filler would drip for ages after the main fill)
• Put food colouring in other toilet to check for leak - no leak into pan
• Isolated cold water supply to Megaflo hot tank (unvented so no cold header in loft) to rule out the hot water system
• Turn off isolator valves to dishwasher, washing machine, other taps etc.

The blasted meter is still moving ever so slightly, so overnight I have checked the meter at 11pm and then 7pm with zero water use and it is registering about 600ml used - so not a lot. Is this minimal movement normal or do I have a leak? There are no stains or sounds etc, I am at a loss so any advice or opinions are gratefully received.

Thanks

 

[brum]

you have a leak somewhere mate..brum

 

[oz-plumber]

The only way you are going to find a leak that small - if there are no visible signs - is to disconnect the house side of the stopcock under the sink and pressure test the house plumbing and then pressure test from the stopcock back to the meter.

Your losing less than 2 litres of water a day, if the leak was inside your property you would have some visible signs of where the leak is.

 

[rpm]

Heard of one this week where the leak was traced to a plastic pipe in a stud wall.

 

[brum]

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I would guess leak in partition or under floorboards down stairs oz is right a pressure test would confirm this I have heard of engineers hooking on CO2 and listening out for the whistle to locate leak position..brum

 

[Chris80]

Thanks guys. To confirm the ground floor is concrete so I am assuming there is no plumbing under there apart from the main water supply? The house is timber frame so I was thinking any leaks would be more evident?

I have had the stop tap off for 3 hours today whilst we were out. Came back and turned back on and ran around listening for water filling. The only area I could hear it was in or around the megaflo. When turning the cold supply megaflo tap off it stopped. This brings me back this but when turning tap off in the last few days the meter keeps turning slowly?

Thanks so far. At the moment I am thinking pressure test (thanks for the advice) but still troubled why the megaflo seems to refill after cutting water supply but the tundish and overflow to outside is dry at all times.

 

[Deleted member 7121]

Thanks guys. To confirm the ground floor is concrete so I am assuming there is no plumbing under there apart from the main water supply? The house is timber frame so I was thinking any leaks would be more evident?

I have had the stop tap off for 3 hours today whilst we were out. Came back and turned back on and ran around listening for water filling. The only area I could hear it was in or around the megaflo. When turning the cold supply megaflo tap off it stopped. This brings me back this but when turning tap off in the last few days the meter keeps turning slowly?

Thanks so far. At the moment I am thinking pressure test (thanks for the advice) but still troubled why the megaflo seems to refill after cutting water supply but the tundish and overflow to outside is dry at all times.

Could be be the hot that's leaking and that's why megaflo is filling

 

[Chris80]

Thanks pipe man. I previously thought I had ruled out hot water leak as when isolating the cold feed to the megaflo the meter stills turns slowly.

 

[lame plumber]

just check if you have any storage tanks in the roof, isolate them first and then see if the movement stops, they are the normal cause of your issue, otherwise check your wcs arent leaking out into the pan via a duff syohon.

 

[Chris80]

Thanks for that lame plumber. But I don't have a loft tank and I have checked all the toilets. I'll have to get a plumber in to find this phantom leak. The others have recommend a pressure test so I'll ask for that. Always like to diagnose things myself but struggling on this one.

 

[IDCHAPPY]

Megaflo unvented hot water cylinder? have you checked the tun dish to ensure its not passing and thus refilling the cylinder?

 

[Chris80]

Hi there. The tundish an outside discharge is dry as a bone. Cheers.

 

[Best]

Hi. If your Megaflow cylinder refills (repressurises) after you turn the water on to it, then if no hot outlet is passing & tundish is dry, it could simply be explained that it's due to the hot water cooling a bit in the unit & this will mean the water pressure will drop a little & unit pressure will need to recover to whatever the pressure reducing valve set limit is.
By that I mean - lets say your prv is set at 3 bar, then that means the cold pressure inside the cylinder is 3 bar. That will rise a little over 3 bar when the Megaflow water is heated & only drop back to 3bar if a hot tap is opened. But hot water at 3 bar will drop in pressure as it cools. Then you turn mains back on & it refills.
Toilets are the biggest cause of water loss.

 

[Chris80]

Thanks Best. That seems really sensible. A query please, if I turn off the main stop tap for a couple of hours and turn it back on you can hear water entering the megaflo (to repressurise by the sound of it), however if I isolate the cold water fill tap (red tap in the picture) but not the main stop tap, even overnight, the water meter keeps moving very slowly. Does this mean that to repressurise the megaflo takes water elsewhere (rather than the cold fill)? Is 40ml to 600ml per hour seem normal? Many thanks.

PS I assume the pressure gauge shown is in fact for the heating pressure.

 

[Best]

Hi Chris. That red headed valve in the picture is a gate valve. It really shouldn't be used on cold supply to your Megaflow IMO.
A brass stopcock or large lever ball valve (full flow) are much better as they will shut off fully. Gate valves are notorious for letting water pass slightly, especially on high pressure mains.
It would be advisable to have the Megaflow isolated so to rule it or hot pipe work out for leaks. I prefer lever valve.
It is also possible that you might have a mixer tap or shower valve letting unbalanced cold mains through its body & this will pass to cylinder & raise the pressure. That however, would simply stop at whatever pressure the mains is, or if high enough, go out tundish.

 

[Chris80]

Thanks Best. So if it was cutting water supply that would be the only feed to repressurise the cylinder as well as replenish water? I have closed (with isolator valves) the hot and cold to 1 mixer shower (fed from the same cupboard) to no avail. But not the other as the valves are under a sealed in bath panel. Is there a way to check the other shower mixer at the mixer control? Cheers.

 

[Best]

Thanks Best. So if it was cutting water supply that would be the only feed to repressurise the cylinder as well as replenish water? I have closed (with isolator valves) the hot and cold to 1 mixer shower (fed from the same cupboard) to no avail. But not the other as the valves are under a sealed in bath panel. Is there a way to check the other shower mixer at the mixer control? Cheers.

Yes, you normally will have an isolating valve for the Megaflow & that gate valve is probably it. Can't rely on it to close fully off as it is only a brass to brass seal inside. Should be better quality valve as I said.
If an unbalanced mixer was passing & check valves were either not fitted or faulty & the incoming cold mains was say, 4 bar, then Megaflow could gradually raise to 4 bar, but not discharge out tundish as 4 bar is still within limits.
My thoughts are you should get the Megaflow closed off using a better valve so you can find out if hot part of plumbing is the problem or not.
You need a G3 plumber to do any work on the Megaflow system

 

[Chris80]

Thanks Best. Much appreciated. So a lever to fully isolate and check if small water usage is hot water/megaflo. But it may be the small usage is expected and not an issue. The tundish has been wet in the past and this was rectified by the usual air gap replenishment.

if the water is relating to a shower mixer is this dangerous?

Cheers.

 

[Best]

Thanks Best. Much appreciated. So a lever to fully isolate and check if small water usage is hot water/megaflo. But it may be the small usage is expected and not an issue. The tundish has been wet in the past and this was rectified by the usual air gap replenishment.

if the water is relating to a shower mixer is this dangerous?

Cheers.

Your shower mixers & mixer taps are supposed to be all balanced hot & cold supplies. Normally that is done from the one source - the units pressure reducing valve. But not all are done that way & houses that have a standard plumbing system converted to an unvented unit often are not balanced. Kitchen sinks are also often not balanced.
If any unbalanced mixers do pass mains water to the unvented unit, it is potentially a hazard & needs sorted. The relief valve will discharge to tundish hopefully, if the pressure gets too high, but that needs a G3 plumber to sort everything.

 

[Chris80]

Ok. I have a boiler service due (through Homeserve) so I'll check if they will also service the megaflo and make these checks. If not arrange this separately. The megaflow is orignal with the house, about 15 years old and we have lived here for a year so I am presuming it was balanced. Cheers.

 

[Chris80]

Hello again Best/All. I have checked with Homeserve and of course the boiler service does not include the Megaflo. So in the meantime I have done a little experiment.

After running a bath for the kids and say 10 minutes later I measured the water meter 0.0001 dial. 5 minutes later 180ml was used (although all taps etc are off). I then turned off the gate valve at the Megaflo, 5 minutes later just 10-20ml was used. Turned the gate valve back on 100ml used in 8 minutes. So the "leak" is definitely the Megaflow drawing in water and the gate tap must never quite shuts hence the slower draw when off.

I believe the water being drawn by the Megaflow slows to a dribble gradually after the water is replaced in the tank (with cold), hence why the water use varies (40ml to 600ml per hour) with so little over night. Does this sound "normal"?

I will get the Megaflow serviced in any event and would ask you (Best) to do it if you were local!

Cheers

 

[Best]

Hello again Chris. At least you are narrowing it down to the hot pipe work side of your plumbing. If you are certain the tundish is totally dry, then maybe the extra water is just replenishing the cooling down of the Megaflow water. If any doubt about slight leaks in hot pipework after the Megaflow, then the hot water pipe leaving the Megaflow could also be fitted with a lever valve by a G3 plumber to prove if any leak is beyond the Megaflow. Hopefully nothing is actually wrong. Water does expand greatly when heated, as will the air in the air gap of the Megaflow probably. Then it reduces as it cools.
I would have gladly helped you, but guess you are on mainland. :smile:

 

[Chris80]

Thanks Best. Great idea about isolating the hot water from the Megaflow. So once the water is diluted with cold from the bottom the Megaflow slowly draws in more to increase to 3bar?

Yes I am SW England matie. Bizarre noone else seems to have noticed this small usage with a Megaflo, I did a lot of searching before posting the query myself. I suppose the meter moves so slowly you wouldnt normally notice.

 

[Best]

Yes, hot water at 3 bar will go to a lower pressure as it will reduce volume in an open cylinder, so in the sealed Megaflow it will just drop in pressure. While the mains remains turned on to the Megaflow, the gradual drop will be topped up again to the 3bar.
Good your are being vigilant and checking for any possible water losses.
One way to test if Megaflow heat drop is having an effect, is to have the unit cold for a day (unheated) and see if meter still passes.

 

[Chris80]

Cheers Best. Sounds like a plan. Should the water get stone cold to test the water usage and presumably the water meter should totally stop moving eventually? At the moment it is only heated 1 hour each evening. So will it need to be running 100% cold to the hot supply to test so may take a day and a half I guess. Cheers.

 

[Chris80]

Thanks Best. I'll give that a go as soon as poss (the wife likes having hot water) and let you know. I think it'll need a day and a half to run totally cold as we only heat for 1 hour each day at the moment.

 

[Best]

Yes, you shouldn't have the water meter moving if no water used. Leaks should not exist, even microscopically on fittings on pipes etc, but things like toilet fill valves and especially toilet flush valves cause a lot of unnoticed leaks on cold supplies.
I am lucky over here, so far, as ordinary households do not have meters and I can use as much water as I want. New valves on roads are fitted though, which have the provision for a meter. :smile:

 

[Chris80]

Thanks for all your advice. Too true about meters. If I didn't have one I wouldn't need to have given this a second thought as there is no sign of a leak. Really seems you've helped me confirm the usage is the Megaflo and likely to be normal. Cheers and I will update this thread in the near future.

 

[Chris80]

Just an update as promised. We went on holiday for a week, had the mother in law in an out to feed the cat etc so couldn't fully monitor the meter. Used around 6 litres per day which seems about right for a one visitor per day. This was the only opportunity to allow the hot water tank to get stone cold. On return checked the meter and again after half an hour or so and no movement at all. This seems to conclude that the water use is a function of re pressurising the hot water cylindricer as it cools. So don't think there is any specific problem. Would be interested to know if other similar systems do the same thing. Cheers.

 

[Best]

Thanks Chris for reporting back.
Yes, all unvented cylinders will do same, because hot water is expanded & will become less volume when cooler. If you put warm water in a plastic bottle & tighten the top on, - you will find the plastic bottle will gradually crush in. If that bottle was an unvented unit, the water would be replaced by the mains joined to it.
You have just been vigilant and found this.

 

[Chris80]

Thanks Best. Another query please. Just today I have noticed water dripping from the water tank overflow outside. Just started as the water is heated. This means time to recharge the air gap. All ok but it is 3 months since the last time and I think 3 months before that. Is this normal? Cheers.

 

[Best]

Hi Chris. You should speak to Heatrae Sadia & ask them about your Megaflow needing the air gap done every 3 months. I hear the floating baffle needs to be checked.
If all else fails, a properly sized external expansion vessel could be fitted by a G3 engineer, but that would be better by instruction of Heatrae Sadia (Megaflow). Your Megaflow I think will have a 25 year warranty providing it has full yearly service record, but this will only cover the main unit.
It is also possible that you have coincidently suddenly too much pressure to the unit, for example, and the proper air gap perhaps still intact and therefore not the cause. Needs a G3 plumber to check. Don't try working on it yourself, except the air gap recharge.

 

[Chris80]

Thanks best. I called megaflo last time and they weren't able to service my tank as it is over 10 years old. Bizarre, but also didn't do 25 year guarantee when mine was installed some 15 years ago. If I recharge it and it doesn't overflow through the tundish this presumably means the pressure is ok? If not is there a register of G3 engineers? Cheers for your help. Much appreciated.

 

[Best]

If you recharge the air gap and the discharge stops for weeks, then the air gap must have been deplemished. But won't prove anything else.
Not sure about how you would get a G3 plumber tbh. A fair number of plumbers probably are now G3 qualified, as they need to be to install and do the paperwork for notification & warranty on unvented cylinders, let alone even service or repair them.
If you still are having bother with the discharge I suggest you go with the idea of a expansion vessel fitted by a G3 person. Megaflows are too expensive & if you need to replace it there are many cheaper units.