Erratic/Over reading Water Meter

[#1]

@idonno 

This is not a calibration error it’s a fault causing an intermittent phantom burst of consumption. Whether a calibration test will find this is debatable.

@MisterW 

Are there by any chance any mains cables running close to the meter?

[#2]

Bit of a long shot maybe - but are there any non-public broadcast type antennas in the vicinity? I'm thinking perhaps a radio amateur using high power?

EDIT: ...or even moderate power if it's beamed in your direction.

[#3]

It could cause cavitation in the water, leading to you measuring air bubbles?

[#4]

Are there by any chance any mains cables running close to the meter?

@Baldrick1  yes, there's a socket for the dishwasher in the same kitchen unit, about 20 cm from the meter. I would have thought that is quite common though. One would hope that the meters would be able to cope with mains electric/magnetic fields ?? The misreading certainly doesnt correlate with when the dishwasher is running though. The socket is on the kitchen ring and I cant of anything in particular that would have been on during the misread periods but I'll certainly consider it during my future checking.

Bit of a long shot maybe - but are there any non-public broadcast type antennas in the vicinity? I'm thinking perhaps a radio amateur using high power?

@198kHz interesting thought... nothing that I'm aware of and no visible antennas I can recall. I'll certainly go and have a good look around though..

For info, yesterdays total consumption was 162 ltrs which is probably about right, the day before was 1852 ltrs according to the meter!!!

Thanks again folks for your thoughts.

[#5]

@MisterW 

I agree it should be able to cope with EM fields, but this is clearly a faulty meter and I was combining my unproven theory that the metering uses magnets in a paddle wheel with likely pulse rates being in the 50. (100 for  power  pulse) band. It could be current in the ring, not just the outlet voltage to the dishwasher that’s being detected.

Have you seen if you can trigger the event by turning the water on then closing the tap abruptly to see if you can find a spot that triggers the fault?

[#6]

Have you seen if you can trigger the event by turning the water on then closing the tap abruptly to see if you can find a spot that triggers the fault?

@Baldrick1  no, it seems to be quite random. What I did prove yesterday, was that when the meter was reading erroneously, turning the kitchen tap on and off stopped the meter reading.

As an aside, it does suffer from water hammer if a tap is turned off quickly.

It could be current in the ring, not just the outlet voltage to the dishwasher that’s being detected.

Agreed, the circuit in question is only the kitchen ring. We had the place rewired and so the kitchen is on its own ring.

[#7]

@MisterW 

I have one of these incorporated in my pipe work, I have a pressure reducing valve with a pressure meter set to 5 bar on my rising main and modern cistern valves would rattle the pressure gauge needle between zero and ten bar about half a dozen times. This device reduces the hammer to a slight blip of about 0.5 bar. It’s sold as a single appliance arrestor but I have taken the view that it’s a single appliance that kicked off the hammering, even if there’s several that can cause it. 
https://www.screwfix.com/p/sioux-chief-dw660-2j-water-hammer-arrestor-bsp/1492r

[#8]

My plumber is supposed to be coming in the near future to fit a Combisave to the hot water feed on the boiler and also repair an outside tap. I had planned to get him to look at the water hammer problem.

Do you just have one of those devices in the main feed ?

[#9]

@MisterW 

The ideal solution is to fit one on the appiance that causes the problem, for example, this fits between the appliance hose and the tap https://www.screwfix.com/p/sioux-chief-dw660-h-water-hammer-arrestor-bsp-connection/9813r. In my case the main problem (but taps being turned off suddenly had the same effect) was the built in cistern in our bathroom where there was no access to the pipework, so it is installed in the pipework about half way between the rising main and the furthest reach of the cold pipework.

My understanding is that these devices consist of a piston that has the water on one side and a sealed air chamber on the other. The water pressure pulse compresses the gas, takes up the reverse flow and releases it as the pressure tries to oscillate and absorbs the energy, so it works a bit like a resistor/capacitor ring/spike filter that we in the business understand.

[#10]

So causing the water to flow backwards, for a short interval.

[#11]

@VileReynard 

Water hammer is caused by water flowing backwards and forwards causing a pressure wave that travels up and down the pipe over a distance. This device dampens this oscillating surge down.

[#12]

Update:

So Severn Trents contractor arrived today to change the meter. Admitted that erratic overreading was a common problem with the existing meter and recorded it as faulty. They are no longer using the electronic type of meter and have reverted to the mechanical type of flow meter. It's still 'smart' and so can be read remotely but doesnt have an lcd display and electronics.

He suggested that ST will reassess previous consumption based on actual consumption from the new meter.

[#13]

Probably a good idea to take a holiday somewhere, to keep your metered water consumption as low as possible.

[#14]

Update:

Got an email from ST this morning :-

The meter at your home was replaced on 15th July 2021 because Technical Upgrade.

AKA 'it was bricked so we replaced it'.

The good news is that they are billing on the basis of 'zero' consumption up to the meter change😁

Checking the new meter over the last week shows it is givng sensible readings, about 120-140 ltrs/day, so about 1m3 a week.

Bottom line is that if you know anyone with the SM100 Electronic type of meter, you might suggest that they check it!

My thanks to all who contributed to the thread.

[#15]

@Baldrick1  thanks for the tip on the water hammer arrestor.

Strangely, most of the problems with taps etc went away when the meter was changed. The washing machine was still ( and always had been, even at the old house ) a problem. So I got one of the 3/4 bsp appliance ones you suggested from the local Screwfix. Took about 10 mins to fit and result no water hammer!.