On Sunday, 5 August 2018 21:23:32 UTC+1, Tim+ wrote:
ARW Wrote in message:
On 02/08/2018 22:13, Tim+ wrote:
Well I replaced the old overheating element with a new adjustable
one that has a boost timer which is a much better
idea.

I was curious as to where the stat was in to old element as it
just looked like a long road with an earth and two power
connections.

After a bit of hacksawing I extracted this which is, I presume, a
70C solid state stat of some sort.

https://photos.app.goo.gl/67pbhzeAExkhMa3i8
https://photos.app.goo.gl/suTh6zDybC5aLshz6

There's also a thermal fuse hidden under the shroud that I didn't
at first spot so I guess that would have provided major overheat
protection.

Oddly, the stat still seems to work although I haven't checked the
temperature it switches off at there's no doubt that the rail
was getting much much hotter than normal.

Is it common (or even possible) for these stats to lose their
"proper" switching temp?



No idea if the stat could lose its proper switching temp but thanks for
the photos.


Well I'm perplexed. There is no doubt in our minds that the towel
rail was overheating.

It had never made "simmering" noises before or heated the room to
a significant extent. It was doing both of those and felt much
much hotter to touch.

Today I got a glass lab thermometer and messed around with hot
water and my multimeter.

At 98c, stat contacts open. 90c, stat open, 80c, stat open. 69c,
stat closed. 70c, stat open.

So, in short, it seems to be behaving exactly to spec (assuming
the 70c printed on the side is the opening temp).

So, why was it overheating? Only thing I can think of is that the
switching temp moves after a period of operation.

Does this sound plausible?

Tim

bimetal stats can become sticky, sometimes sticking shut.


NT