immersion water suddenly getting a lot hotter

[percepts]

Economy 7 immersion heater water suddenly getting a lot hotter. I'm guessing either thermostat has failed or heater is on the way out.

So question is, what is the best course of action? Just change thermostat if I can source one for a Redring P14T or go ahead and replace the whole heating element ( which is probably 15 years or more years old ). Second option is more work but should last longer I guess. What do you rekon?

Thanks

p.s. we have soft water and get no limescle build up, Just brown staining in kettle which lasts for many years.

 

[Whitespirit66]

Likely to be a failing thermostat, so try a new one. Will save you some money and a lot of aggro if that's all it is.

 

[percepts]

Likely to be a failing thermostat, so try a new one. Will save you some money and a lot of aggro if that's all it is.

Any idea where I can find one? Been looking on web and can find complete units but not just thermostat.

If was going to replace whole element then I would get the newer Redring P14DC unit but if I buy a P14T unit then I could take the thermostat from that but am lumbered with older unit if I need to replace whole thing. Can thermostats actually be bought separately?

 

[JohnD]

yes.

http://www.screwfix.com/search.do;j...h_search=immersion+thermostat&fh_view_size=20

 

[Whitespirit66]

Any plumbers merchants will sell thermostats. You don't need a Redring, the element is a standard 14" 3Kw model.

 

[dcawkwell]

Failing thermostat. Cheap to swap out.

 

[percepts]

Thanks guys, I know where I'm going now. But first I turned down thermostat just to see if it makes a difference but I doubt it.

 

[JohnD]

if you are on economy 7, you may (should) have either quite a long immersion heater element going in from the top, or quite a short one going in from the side. Best to take out the old thermostat before buying a new. The stat slides into a sealed tube, so no water leaks out when you withdraw it. If unsure, you can poke down the tube to see how long it is.

Modern stats have an overheat cut-out to prevent boiling and scalding, so may not be identical to your old one.

Taking out a very old immersion heater that has seized into place can be difficult as excessive force can bend or tear the (thin, weak) copper cylinder. The stat is easy.

 

[percepts]

New thermostat bought and installed. I'll find out tonight / in morning if its working properly.

One further question. The thermostat wasn't marked to say which side the live wire goes in. The unit is almost identical to old unit and I couldn't remember which side live wire went. However, seems to only fit well one way. Anyhyhow I've drawn a diagram. Do you think this is correct side for live wire? Does it matter which side it goes in?

thanks

Untitled

• percepts
• 4 Apr 2013
• 1

 

[percepts]

Forget that, I have the answer. I opened up the old thermostat.
It doesn't matter which side the live wire goes in cos the on/off switch is controlled by expansion and not electronics.
Expansion sets off a clicker switch. So it kind of begs the question, how is it that a thermostat like this can go wrong? There is an adjustable screw which the temp setting controls so that could be adjusted but why would it go wrong? Possibly clicker unit weakening.
Anyhow we'll see how new unit works tonight.

 

[mogget]

I think the contacts arc and weld themselves together, thus failing in the closed position.

There was a case a few years ago when this happened, and the water boiled. It went up the vent pipe and filled the (plastic) attic tank with boiling water. The tank split and the water came through the ceiling, tragically killing the baby sleeping in the room beneath. That's why the new stat will have a little reset button, it is fitted with a secondary stat in case the first one fails.

 

[percepts]

Yes the instructions mention that but I see no button on it. It says it's recessed but It looks identical to old unit except for colour.
No worry I don't have a baby

 

[percepts]

fixed. Normal water temp restored. Well it was a bit low today but I tweaked that so hopefully tomorrow temp should be about right.

Thanks all...