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Topic Title: Unvented Electric Water Heater.
Topic Summary: Questions.
Created On: 04 October 2017 09:51 AM
Status: Read Only
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 04 October 2017 09:51 AM
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Zoomup

Posts: 3286
Joined: 20 February 2014

An ELSON-ZIRCON 210zd unvented domestic hot water cylinder has had problems with the safety thermostats tripping off. The system is about a year old. The stats are of the bulb on the end of a capilary tube type. Two bulbs per stat, the first for the functional stat contacts and the second for the safety limit cut out contacts presumably. There are two stat pockets on the immersion heater head.

Both the top and bottom limit safety stat cut outs had tripped off. The elements are in good working order. Why would this happen? The functional stats were set at about 75 per cent maximum temperature.

Also, the tenant is concerned that the system has not been installed by a qualified installer. The installation label on the tank has not be completed at all. A plumber replaced a fitting on the top of the tank as he said that the part could allow a discharge of hot water, so fitted a solid tee fitting.

It all seems a bit amateurish.

Any thoughts please?

Bye,

Z.
 04 October 2017 10:27 AM
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AJJewsbury

Posts: 15849
Joined: 13 August 2003

A plumber replaced a fitting on the top of the tank as he said that the part could allow a discharge of hot water, so fitted a solid tee fitting.

If someone's really removed the temperature & pressure release valve from an unvented cylinder, then they want putting up against a wall and shooting - as they're turned a domestic appliance into potential bomb. (Those of us old enough to remember reports of back boiler steam explosions when a family returned home during cold spell and lit the fire - which literally demolished half the house - wouldn't underestimate the risk there).

On the basic question though, are there any other sources of heat? - e.g. connection to a gas boiler or solar or a even a solid fuel boiler? If so those could continue to raise the temperature even when the immersion etc have switched themselves off, so triggering the safety cut-outs. Tread carefully - there's a lot to get right with these things for them to be safe.

- Andy.
 04 October 2017 10:55 AM
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Joined: 20 February 2014

There seem to be automatic release valves connected to a tundish from pipework on the side of the cylinder. I do not tink that there is any other form of heating, just electric.

Z.
 04 October 2017 11:45 AM
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AJJewsbury

Posts: 15849
Joined: 13 August 2003

That's a relief - so what did the "plumber" replace with a solid fitting then? If it was the cold water expansion valve (intended to protect the system from overpressure if the pressure reducing valve in the supply malfunctions) it's perhaps not as serious, but still not right. http://www.elsonhotwater.co.uk...36006102_issue_03.pdf

My only remaining thought is that either the normal thermostat isn't working correctly - i.e. allowing the immersions to heat beyond the intended temperature, or the safety cut-out is over eager - cutting out at too low a temperature. The former might be a fault in the thermostat itself or something else that's isolating it from the heat from the immersion - not making proper thermal contact with it's pocket or something like that. The cylinder is full of water isn't it??

- Andy.
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