Economy 7 Cylinder - No hot water

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Hi
Looking for some help with regards to an Economy 7 system

I have a two part hot water cylinder with a day rate and night rate switch.

I can't get any hot water out of the system at all. I have tried both switches so don't think it would be the elements as both don't work. Nothing has tripped on the main board it just seems it has stopped heating the water.

I've read that it could be a thermostat but would both go at exactly the same time?

Any help appreciated.

Thanks
 
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Most modern immersion heaters have two thermostats:

1. The normal one which turns off when the water is hot enough and back on when the water has cooled.
2. An "overheat" one, which turns off when the water exceeds a manufacturer determined temperature (normally around 85 to 90 degrees), but has to be manually reset to back on.

Look for a small black or red plastic button on the head of the immersion heater. Don't forget you'll have to take the cover off, and that will expose bare terminals with mains voltages present, so make sure BOTH immersion switches are off, and test with a multi-meter before touching anything. You should have zero volts between live and neutral, between live and earth and between neutral and earth. Don't forget the Economy 7 voltage will only be present between about 11pm and 5am, so do all work outside these times unless you are absolutely sure the Economy 7 (normally lower immersion heater) is off.
 
Thanks for your help!.
The cylinder has one element at the top and one at the bottom (top one wired to night switch, bottom to day switch)

I have taken the covers off each of the elements to check. They both have thermostats on them.

Is one of these thermostats the overheat one, so if this one trips then the whole system shuts down?. Just unsure why one tripping would shut the other off too

I will try a reset on each of the thermostats to see if that works.
Each thermostat is set to 60 degrees, would this be correct?

I guess I may need to replace the thermostats if the reset doesn't work?

Do you think this is not an element issue if both are down?

Thanks again!
 
EACH immersion heater is likely to have two thermostats (so four in total), one with a dial with numbers on it (the "normal" one) and one which is reset by pressing a button (the "overheat" one). The button may be recessed and require something like an straightened paper clip to access.

If the water overheats for some reason, then one or even both overheat thermostats may trip, as they are temperature dependent. If both trip it would explain the lack of water heating.

If you know how to use a multi-meter there are further tests you can do. However, some of these require the power to be switched on, so you need to be fully aware of what you are doing, and extremely careful:

1. With the power ON - Test that there is 230V between live (should be brown wire) and neutral (should be blue). (Multi-meter on AC voltage range, setting greater than 230V (usually 750V). If not there is a fault external to the immersion heater. Clearly, for the Economy 7 immersion, this can only be done during the powered hours.
2. With the power OFF:
2a. Set the multi-meter to a low resistance range (say max 100ohms). Measure the resistance of the immersion element, which should be around 8 to 12 ohms (cold). The immersion element is normally connected directly to the neutral (blue wire) and to one side of the thermostat, the other side of the thermostat being connected to live (brown wire). If resistance is low, the element has short circuited. If resistance is high, the element is open circuit. In either case the element must be replaced, which requires the cylinder to be drained (at least partially) and is only a DIY job for the very experienced.
2b. Set the multi-meter to its lowest resistance range (continuity check). Connect a lead to each side of the thermostat, then operate the thermostat. At low, the thermostat should be open circuit (infinitely high resistance), at high temperature (or somewhere between low and high) it should indicate very low (.01 or less) ohms, and depending on the meter, give a buzz for continuity. If neither happens, the thermostat must be replaced. This can be done fairly easily, but requires a reasonable knowledge of things electrical.

If you do any work on the immersion heaters be very careful that power is isolated (except for 1. above) and work with extreme care. If you undo any of the cable connections to an immersion heater it is essential that they are done up again properly and tightly, otherwise there can be arcing which can lead to severe overheating and fire.

I'd recommend you restrict yourself to checking, and if necessary re-setting, the overheat thermostats. If you post a picture of the immersion heaters, with the covers removed, it would help in determining if they do have overheat thermostats or not.

Finally, the normal connection is Economy 7 to the lower immersion heater, so that it heats up the whole cylinder at the overnight rate, and the top heater connected to normal rate electricity for a "top up" of heat to the top third of the cylinder only.
 
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EACH immersion heater is likely to have two thermostats (so four in total), one with a dial with numbers on it (the "normal" one) and one which is reset by pressing a button (the "overheat" one). The button may be recessed and require something like an straightened paper clip to access.

If the water overheats for some reason, then one or even both overheat thermostats may trip, as they are temperature dependent. If both trip it would explain the lack of water heating.

If you know how to use a multi-meter there are further tests you can do. However, some of these require the power to be switched on, so you need to be fully aware of what you are doing, and extremely careful:

1. With the power ON - Test that there is 230V between live (should be brown wire) and neutral (should be blue). (Multi-meter on AC voltage range, setting greater than 230V (usually 750V). If not there is a fault external to the immersion heater. Clearly, for the Economy 7 immersion, this can only be done during the powered hours.
2. With the power OFF:
2a. Set the multi-meter to a low resistance range (say max 100ohms). Measure the resistance of the immersion element, which should be around 8 to 12 ohms (cold). The immersion element is normally connected directly to the neutral (blue wire) and to one side of the thermostat, the other side of the thermostat being connected to live (brown wire). If resistance is low, the element has short circuited. If resistance is high, the element is open circuit. In either case the element must be replaced, which requires the cylinder to be drained (at least partially) and is only a DIY job for the very experienced.
2b. Set the multi-meter to its lowest resistance range (continuity check). Connect a lead to each side of the thermostat, then operate the thermostat. At low, the thermostat should be open circuit (infinitely high resistance), at high temperature (or somewhere between low and high) it should indicate very low (.01 or less) ohms, and depending on the meter, give a buzz for continuity. If neither happens, the thermostat must be replaced. This can be done fairly easily, but requires a reasonable knowledge of things electrical.

If you do any work on the immersion heaters be very careful that power is isolated (except for 1. above) and work with extreme care. If you undo any of the cable connections to an immersion heater it is essential that they are done up again properly and tightly, otherwise there can be arcing which can lead to severe overheating and fire.

I'd recommend you restrict yourself to checking, and if necessary re-setting, the overheat thermostats. If you post a picture of the immersion heaters, with the covers removed, it would help in determining if they do have overheat thermostats or not.

Finally, the normal connection is Economy 7 to the lower immersion heater, so that it heats up the whole cylinder at the overnight rate, and the top heater connected to normal rate electricity for a "top up" of heat to the top third of the cylinder only.

A 3kw element is normally about 19Ω.
 
Thanks for the lengthy reply. It is hopefully a great help!

I am going to try the reset this weekend.
Below are the two exposed elements (thermostats) Should I turn the temperature down on these if they are overheating?

Top element


Bottom Element


Thanks!!!!
 
1. Terrywookfit is right. I meant to type resistance range 18 to 20 ohms.
2. I think, but can't be certain, both immersions have overheat thermostats.
3. If the Backer (blue) one has, it will need a paper clip or similar pushed into the small hole by the 60degree mark.
4. If the Sunvic (red) has, it will need something pushing into the rectangular hole above the 0degree C mark.
5. You don't need to reset the normal thermostats. 60 degrees is about right for hot water.
6. When pressing the overheat thermostat reset buttons, you should feel spring pressure when you first push, and then feel or even hear a slight click when it resets.

Make sure the mains to both immersions is off when you do the reset.
 
Hi
Just an update to this
I tried the reset. I heard a slight click when pressing.

The red thermostat seemed loose and I seemed to be able to push it in and out and move the element (this was the top one)

I have not managed to get any hot water since the resets. Do you think this could be faulty thermostats? Not sure if it's worth trying to replace those before I call anyone in

Thanks
 
It could be faulty thermostats, but the only way to tell is to test them - point 2b in post #4.
It could be a number of other things, and again the tests outlined above will confirm what the problem is.
The thermostats fit loosely inside "pockets" which are closed lengths of pipe (often copper) sitting inside the cylinder, but with the open end sealed to the body of the immersion heater. Thus you can change the thermostat without draining any water.
As a further check, make sure that the immersion heaters are run from the main consumer unit (the economy 7 one will probably be from a different source) and not from an additional unit.

Unless you have both the equipment and the skills to carry out the tests suggested above, I think it is time for you to call someone in.
 

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