Immersion Stat. Fails to On?

Discussion in 'UK DIY' started by Sam Norris, Dec 10, 2003.

  1. Sam Norris

    Sam Norris Guest

    Hi,

    We use the immersion heater on the hot water cylinder sometimes. The
    other day the 18" thermostat broke and I replaced it this morning. What
    interested me was the old one failed to `on', so the heater heated lots
    until it was making such a noise that we noticed. I'm surprised the
    failure state isn't off. What would happen if I didn't turn it off?

    Also, on removing the old one, the plastic casing around the terminal
    for one of the wires is distorted as if it had melted slightly. Perhaps
    that occurred at the same time as the stat. failed.

    Both new and old are 16A on a 3kW heater.

    Sam.
     
    Sam Norris, Dec 10, 2003
    #1
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  2. Sam Norris

    Ed Sirett Guest

    On Wed, 10 Dec 2003 16:18:01 +0000, Sam Norris wrote:

    > Hi,
    >
    > We use the immersion heater on the hot water cylinder sometimes. The
    > other day the 18" thermostat broke and I replaced it this morning. What
    > interested me was the old one failed to `on', so the heater heated lots
    > until it was making such a noise that we noticed. I'm surprised the
    > failure state isn't off. What would happen if I didn't turn it off?
    >

    The water would boil, the space where the cold tank would fill with much
    steam/condensation/humidity the cold tank would heat up.

    Eventually if the cold tank was inadequately suppported and/or missing its
    lid it might collapse and drop scalding water below. This is the way
    someone was killed recently.

    However the noise is enough to make any resonable curious person switch
    off the heater.

    --
    Ed Sirett - Property maintainer and registered gas fitter.
    The FAQ for uk.diy is at www.diyfaq.org.uk
    Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
    Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
     
    Ed Sirett, Dec 10, 2003
    #2
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  3. Sam Norris

    Ed Sirett Guest

    On Wed, 10 Dec 2003 16:29:11 +0000, Christian McArdle wrote:

    >> We use the immersion heater on the hot water cylinder sometimes.
    >> The other day the 18" thermostat broke and I replaced it this
    >> morning. What interested me was the old one failed to `on',
    >> so the heater heated lots

    >
    > Failure modes of thermostats allow failure to occur to the on or off
    > position.
    >
    > When installing an immersion, it is a good idea to select one with two
    > thermostats. One will be a normal one set to the required temperature. The
    > other should be a manual reset one set 10 degrees higher. This way, the
    > consequences of thermostat failure are reduced. Unvented cylinders are
    > required to have such immersions, but they are a good idea for any cylinder.
    >

    What's more the second thermostat is required to be of the manual reset
    type.




    --
    Ed Sirett - Property maintainer and registered gas fitter.
    The FAQ for uk.diy is at www.diyfaq.org.uk
    Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
    Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
     
    Ed Sirett, Dec 10, 2003
    #3
  4. Sam Norris

    Ed Sirett Guest

    Ed Sirett, Dec 12, 2003
    #4
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