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

 

[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.