Unable to remove heating element from HW cylinder.

[L_Plate]

I have decided to try to resolve the operational problems on this thread in order to avoid confusion and the need for repetition.

Having replaced the heater element in the HW cylinder there are a couple of issues. Firstly, though the replacement element is a 14" 3kw, ie exactly the same as the one it replaced, it gives rather less hot water. I have checked the thermostat which is similarly set to 60ºc. There is one physical difference though, the new element has quite a bit less tubing than the old. Would this account for any difference in heating performance?

Secondly, an airlock has occurred in the section of pipe that supplies the kitchen. The supply to the bath and basin is perfectly acceptable. The tapping on the cylinder for the HW is on the side, not out of the top with the vent pipe. A 22mm tee fitting is connected to the cylinder for the HW, one side going to the bathroom, the other to the kitchen. I have tried running water out of the cylinder so the water level falls below that of the HW connection and then trying to fill from the cold supply on the mixer tap in the kitchen (blocking the spout).

Any suggestions, please, would once again be very welcome. Cheers.

 

[JohnD]

I am not a plumber, but a 14" immersion element seems very short to me. Mine is 27".

An element will not heat any water lower than it reaches (all the hot water rises to the top) so once yours is hot about 14" from the top, it will switch off.

 

[L_Plate]

I am not a plumber, but a 14" immersion element seems very short to me. Mine is 27".

An element will not heat any water lower than it reaches (all the hot water rises to the top) so once yours is hot about 14" from the top, it will switch off.

I understand that, JohnD. What I have here is a cylinder designed to have two 14" elements. The prevailing wiring is only sufficient to supply the upper element so the performance has always been rather limited. For some reason the new element is even less effective than the old and I am assuming that this might be because the amount of tubing in the construction of the orig element is greater than that of its replacement.

 

[JohnD]

don't know then. Unless possibly when it was screwed in, the orientation of the cap meant the thermostat is at a higher level with the new one than it was with the old one?

So is yours the Economy 7 design of cylinder, where the elements go in through the side rather than through the top?

How does the idea of changing the cable so it reaches the other element appeal? You can get a 2-way Immersion switch (sink and bath) that will switch alternately between the upper and the lower element. You just need some 1.5mm Heat Resistant 3-core cable (usually the Silicone Rubber type is used)

 

[L_Plate]

don't know then. Unless possibly when it was screwed in, the orientation of the cap meant the thermostat is at a higher level with the new one than it was with the old one?

So is yours the Economy 7 design of cylinder, where the elements go in through the side rather than through the top?

How does the idea of changing the cable so it reaches the other element appeal? You can get a 2-way Immersion switch (sink and bath) that will switch alternately between the upper and the lower element. You just need some 1.5mm Heat Resistant 3-core cable (usually the Silicone Rubber type is used)

Yes, John, I think the cylinder must be designed for Economy 7 usage. What confuses me, though, is that it has not been wired up for this type of set-up ie as you describe with a 2-way switch etc. The existing connection comes off of a 16amp mcb at the CU. It then runs to a timer (next to the CU). This is connected by 2.5mm cable which runs up into the loft to the douple-pole switch. From the dps two immersion heater flexes are connected; one flex to the new (less than effective) upper element; the other flex has been isolated. The lower element remains unconnected. Clearly it was not possible to connect the lower element also as this would require 13amps for each element. I have then a couple of questions:

1) Using a 2-way switch is it possible to have two elements on together or is there only a choice between one element or the other?

2) If a 2-way switch is used to alternate between either element does each element require a double-pole switch?

 

[JohnD]

only one on at a time

the switch is normally a 2-gang one:

- On/Off
-Sink/Bath

where the "on-off is (should be) the DP switch

if for some reason you can't get hold of this kind of immersion switch (it is a fairly standard type) then you could use two switches, one DP on/off and a separate 2-way changover, or assemble it as a Gridwitch.

It must be arranged so you can't have them both on at the same time

 

[L_Plate]

Thanks very much, John. Good information.