immersion heater

[John.Stitch]

Is this one U/S
30 years old not used too often in a high scale (Limestone) area.
Two switches.
One by the back door one in the airing cupboard.
Both have to be on for the EH to work.
One in the airing cupboard is on, turn the other on and the fuse goes pop.
Checked the wiring on both switches are they look OK.
Removed the cover on the EH and removed the neutral wire and put a multimeter across the terminals to get a resistance of 3.2Meg.
Or could it be the themostat?

 

[Spark123]

3.2M doesn't sound good for an element, at that sort of age it probably won't have a safety cutout so worth replacing it anyway.

 

[flameport]

put a multimeter across the terminals to get a resistance of 3.2Meg.

Which terminals?

If L&N, the resistance should be a few tens of ohms, certainly not above 100.

If L&E or N&E, 3.2meg would be acceptable according to the regs, but in reality it suggests the element is failing. That assumes it was measured with an insulation resistance meter, which uses 500 volts during the test.
If you measured that with a normal multimeter, the real reading with any significant voltage applied is probably much lower than that, and the element is broken.

 

[John.Stitch]

The live and neutral terminals were the ones I probed.
Could not see the point of testing the L-E or N-E
I do not know the spec of the meter but it is quite a good one.

 

[333rocky333]

Most elements split and short to earth that is what blows the fuse.
An element is unlikely to short L to N.