Testing the Economy 7 supply

[Mike4]

I fix boilers for a living, and although I'm a gas bod I'm getting more and more calls these days to Economy 7-powered thermal-store water heaters.

I currently have one that fails to heat up overnight, and I'm mystified. I've checked over-all continuity by taking the cover off the consumer unit and measuring the resistance across the (night-time) live rail into the circuit-breaker and neutral, and found about 18 Ohms, which seems about right. This indicates to me that continuity is fine. There is aso a night storage heater that appears to heat up correctly overnight. (I was testing with this isolated! With it connected, the result is about 9 Ohms.)

BUT the thermal-store hot water cylinder doesn't heat up overnight. Not possible, but that's what happens, grrrr... Any suggestions anybody?

Is there any device or sensor I can attach to the E7 supply and to the input terminals of the thermal store that will record whether the E7 power came on during the night? These are elderly customers in sheltered accommodation and I won't be welcome there testing between midnight and 7.00 in the morning (as if!)

All advice most welcome.

Cheers, Mike

 

[Steve]

element goosed?
local fuse? (FCU?)

If the heater heats ok during the night, then you know E7 is working. I'd go for a burnt out element and/or blown fuse at the boiler.

 

[ricicle]

element goosed?
local fuse? (FCU?)

If the heater heats ok during the night, then you know E7 is working. I'd go for a burnt out element and/or blown fuse at the boiler.

If there is continuity of about 18 ohms then the element sounds ok and if tested from the CU then the fuse also sounds ok (fcu not normally fitted to immersion)

Is the stat faulty/set too low.This would allow continuity in the daytime when tested but break circuit when powered up and water starts to heat up but not enough to notice the heat in the morning

p.s Are you sure the 18 ohms you are getting is the water heater circuit

 

[Mike4]

Thanks for your replies.

If there is continuity of about 18 ohms then the element sounds ok and if tested from the CU then the fuse also sounds ok (fcu not normally fitted to immersion)

That is my thinking too. There is 18 ohms on the immersion element terminals, on the immersion heater cable (i.e. with the thermostat in the circuit) so that's why I went right back to the CU, ands still found 18 ohms.

Is the stat faulty/set too low.This would allow continuity in the daytime when tested but break circuit when powered up and water starts to heat up but not enough to notice the heat in the morning

p.s Are you sure the 18 ohms you are getting is the water heater circuit

Good point about the thermostat being well out of range. Unlikely as I've replaced the element and stat anyway, but whatever it is, it is an unlikely fault. All the likely stuff has been ruled out.

I'm fairly certain I'm testing the correct circuit. there are only two. A storage heater and the immersion heater. 9 ohms at the CU with both on, 18 with either of them turned off. 9 ohms is what I'd expect a combined 6kW load to measure.

I'm beginning to wonder if it's something really stupid, the customer is turning it off at night, or something.

Cheers, Mike

 

[Belle427]

im familiar with e7 but how does it kick in? is there a timer at the main premesis board?

 

[bernardgreen]

Is there any device or sensor I can attach to the E7 supply and to the input terminals of the thermal store that will record whether the E7 power came on during the night? These are elderly customers in sheltered accommodation and I won't be welcome there testing between midnight and 7.00 in the morning (as if!)
Cheers, Mike

A mechanical electric clock connected to the ecomony 7 supply. Note the time on it when you install it. Next day see how far the hands moved. That will be the number of hours you had power.

Or invest in a 230 v time elapsed meter if this is a frequent problem.

If you suspect that they are turning it off. ( not unknown as people worry about costs ) a bit of discretely place WhiteTack ( or bluetack ) will show if switches thermostats have been moved. Old people can be too proud to admit they turn off to save money.

 

[THRIPSTER]

Are the heaters on a dedicated electrical supply? If so, what about a faulty breaker?