DIY Doctor

Replacing element in unvented immersion system

Postby Charles Darke » Sun Mar 18, 2007 4:33 pm

I bought a new flat and I think there's a problem with the hot water because it is piping hot. There's no way to turn it off even when we turn the timer to off, the water is still being heated by the immersion heater (the immersion is the only way of heating water in the house).

Can a faulty thermostat do this? I noticed that there was leaking in the element assembly and the element place assembly is significantly rusted. I'm not sure if this could have shorted the timer device.

Anyway, last week, the heater stopped working and the tank is stone cold. Either the thermostat died completely and failed safe, or the cut-off has kicked in to turn everything off.

The element is mounted on the side about 1/3 from the bottom of the tank. The whole system is an unvented system with a pressure tank on the top. Is replacing the element a suitable DIY job?

I imagine it's just a case of loosening the element with a giant spanner, then draining the tank to below 1/3 level and then taking out the old element completely and replacing it with the new one (I'm assuming element, thermo and cut-off are all integrated).

Is there anything I need to watch out for? I've never dealt with a pressurised system before. Also, how much should it cost to get this thing done professionally?

Lastly, is it worth replacing the whole tank. If so, how much more should this cost? Thanks for any help/advice.
Charles Darke
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Simply Build It

Postby stephen.s » Wed Mar 21, 2007 9:10 pm

Strictly speaking, the law states that you have to be qualified to work on unvented systems. also, not an immersion heater will do, they are a different size to that of a traditional vented system. they also have a built in thermostat. in order to drain the system down, you would have to identify either the pressure relief valve or the expansion relief valve and manually operate them. the high energy cut off if non-self resetting so checking this would be a sensible start, although if this has tripped, there will be a reason why and you would need to identify this reason. the immersion heater for your cylinder must be replaced like-for-like as each manufacturer has their own for each of their different cylinders. replacing the whole thing would cost a fortune. as for the cost of getting the problem sorted professionally, if it was me doing the job, i woud be looking at around £50 - £70 labour charge depending on what exactly needs doing, plus parts. sorry i cant be of more help than this, but unvented sstems can pose a significant risk if certain aspects are over looked. my avice to ou woud be to look in the yellow pages for an un-vented specialist and call them to do the job, or if you are local to me, you could alwas give me a shout! By the way, cant remember if i mentioned, but replacing the whole cylinder would cost an absolute fortune in comparison to fixing it!!! See if you can find any paper work and have a look if it is still under warranty, if it is, let the manufacturer deal with it! Good luck[/quote]
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