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• FIRST POST
• Yellabowley
• 7th Dec 18, 11:02 AM
• 101Posts
• 20Thanks
Yellabowley
Morning all,

I moved into a new build in February and due to having a wife and two kids and working shifts I always used to run my hot water on constant as I need it at all times of the day.

After two months we discovered an issue and a Kingspan engineer came to look at our cylinder. He found out that the builder’s electrician had wired it incorrectly and had bypassed the thermostat. As such it never recognised that it was up to temperature and had been heating the water 24 hours a day for two months causing the safety valve to repeatedly expel water. Our first gas bill showed that we owed £700.

I’m now looking for compensation from the builder (they’ve admitted the mistake but are arguing the amounts) but cannot find efficiency ratings or similar specifications that would tell me how much gas the cylinder would use while running. I tried calling Kingspan but the call taker spoke to a manager and neither knew how to find out. The cylinder is model number TXN210PT0ERP if that helps.

We’ve tried looking at gas usage as the obvious answer but this is further complicated by a disputed start read on moving into the property.

Page 1
• Barneybear1
• 7th Dec 18, 12:50 PM
• 15 Posts
• 6 Thanks
Barneybear1
The following formula is used to calculate the power of heating element needed to heat a specific volume of water by a given temperature rise in 1 hour.

volume in litres x 4 x temperature rise in degrees centigrade / 3412
You can extrapolate your volume,temp rise,time taken and factor in your boiler efficiency to deem kWh needed
• ajbell
• By ajbell 7th Dec 18, 2:41 PM
• 1,033 Posts
• 3,329 Thanks
ajbell
Did you not notice the water was almost boiling?.
When my iboost failed I remember seeing that my solar panels had put 16 kwh into hot water in 1 day and I could hear the water bubbling.
Rather than getting money back for the wasted energy I would be complaint about the safety aspects of boiling water and dumping unlimited amounts of energy into the water tank.
Last edited by ajbell; 07-12-2018 at 4:11 PM.
4kWp, South facing, 16 x phono solar panels, Solis inverter, Lincolnshire.
• Hengus
• By Hengus 7th Dec 18, 4:12 PM
• 6,840 Posts
• 4,395 Thanks
Hengus
The OP can take some comfort in the fact that the PRV at the top of the tank has been working as it should. That said, I would be demanding that the whole installation is checked by a G3 qualified gas safe engineer. PRVs are not designed to be in constant use and there is likely to be damage around the seal due to hardness deposits in the water.

To put the OP's problem into context. We have a 250L hot water unvented cylinder. The cost of re-heating this for a month on gas was less than £10 a month (6kWhs per day) in August and September. OP - if you have a large unvented cylinder then you are wasting considerable amounts of energy by leaving the cylinder on constant re-heat. The cylinder should be sized for your property. We heat our cylinder once a day and we never run out of hot water.
Last edited by Hengus; 07-12-2018 at 4:37 PM. Reason: typo
• Anthony C
• 8th Dec 18, 11:31 PM
• 46 Posts
• 2 Thanks
Anthony C
Hot water cylinder
The average energy used by a gas boiler for a standard size hot water cylinder is about 6kWh from cold for about 1 hour.
If a boiler is left on constant it will cycle on-off to maintain the flow and return pipework temperature, say 1kWh max.
That's why it's important to insulate the pipework and the cylinder, that includes the pipe from the cylinder to the taps for about 1 metre. It's worth extra insulation at the top of cylinder where the heat loss is greater.
• Hengus
• By Hengus 9th Dec 18, 10:02 AM
• 6,840 Posts
• 4,395 Thanks
Hengus
Hot water cylinder
The average energy used by a gas boiler for a standard size hot water cylinder is about 6kWh from cold for about 1 hour.
If a boiler is left on constant it will cycle on-off to maintain the flow and return pipework temperature, say 1kWh max.
That's why it's important to insulate the pipework and the cylinder, that includes the pipe from the cylinder to the taps for about 1 metre. It's worth extra insulation at the top of cylinder where the heat loss is greater.
Originally posted by Anthony C
You are correct but your comparison does not match the situation that the OP has found himself in. The normal thermostat has been bypassed and the safety cut out has been working via what is known as the Temperature Pressure Relief Valve. The. TRPV is usually set at 90C. Once it operates, water from the cylinder is expelled via a tundish to a runaway pipe. Think of it like a kettle that you boil to 90C. Once it reaches 90C, the kettle starts to leak but is refilled from the cold tap. The constant egress/ingress cycle continues and the immersion heater continues to reheat the cylinder. The ‘problem’ for the OP to answer is why it took so long to notice the problem? The water coming out of the taps would be close to boiling and there would be evidence of expelled water on the outside wall of the property.
• Anthony C
• 9th Dec 18, 1:17 PM
• 46 Posts
• 2 Thanks
Anthony C
Did you not notice the water was almost boiling?.
When my iboost failed I remember seeing that my solar panels had put 16 kwh into hot water in 1 day and I could hear the water bubbling.
Rather than getting money back for the wasted energy I would be complaint about the safety aspects of boiling water and dumping unlimited amounts of energy into the water tank.
Originally posted by ajbell
Thanks
Just to clarify, I was saying what the average is under normal control
Boiler stat 65C
Hot water cylinder stat 55C (legionnaires)
• coffeehound
• 9th Dec 18, 1:35 PM
• 2,149 Posts
• 3,382 Thanks
coffeehound
OP it is more down to how much gas the boiler used rather than the cylinder details. The cylinder was telling the boiler it need continuous heating, so the boiler will have been responding to the maximum extent limited by some factors such as the setting on the boiler dial, and how much of its output was directed to the central heating. So take a note of the boiler dial setting.

Some systems prioritise HW over CH. Did you notice that the CH wasn’t working properly, not getting properly warm?

In any case, the most logical way to go is to take actual gas meter readings now if you haven’t already, and then find your normal usage for the next several weeks. Calculate what your excess usage was due to the wiring fault and invoice the culpable party accordingly.
• tastyhog
• By tastyhog 9th Dec 18, 4:36 PM
• 550 Posts
• 1,022 Thanks
tastyhog
Also take in to account the water usage, if on a meter which it likely is if its a new build, which could be quite considerable as you essentially have a 24/7 leak and at £5 or so per cubic meter of water / sewerage it will quickly add up if its exoelling water all day every day.

Have you had a water bill yet?
• coffeehound
• 9th Dec 18, 4:51 PM
• 2,149 Posts
• 3,382 Thanks
coffeehound
I’m not sure there would have been large amounts of water being expelled. As i understand it, the maximum temperature of the boiler’s primary circuit would be set by the control dial and the boiler would have modulated on and off to maintain that temperature. If that temperature were say 70 deg C then the cylinder water would not go above that temperature.
• coffeehound
• 10th Dec 18, 12:25 PM
• 2,149 Posts
• 3,382 Thanks
coffeehound
This must be the electric immersion heater rather than the gas boiler, mustn’t it? Perhaps the OP is in for a bigger shock when he sees the electricity bill. A 1.5 or 3 kW element on full-time for two months...
• coffeehound
• 10th Dec 18, 12:45 PM
• 2,149 Posts
• 3,382 Thanks
coffeehound
... which funnily enough would be about £700.
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