White meter and immersion heater

Hi folks,
I have a retirement flat with Economy 7 heating and hot water. I have a single meter with two readouts - 1 low, 1 normal. Connected is a timer which switches the supply between low and normal at approx. 8.45am and 11.45pm. Hot water is via a cylinder which has 2 immersions, one at the bottom and one at the top. The bottom one is connected to a cable and a simple on/off wall switch labelled Off Peak and the top one is connected to a similar cable and switch labelled Water Boost.

I had expected that keeping the Off Peak switch on all the time would heat up the water between 11.45pm and 8.45am to whatever temperature the immersion thermostat was set at and it would switch off so that water didn't get too hot. Unfortunately, that doesn't happen. The immersion switches on at 11.45pm as it should and it heats the water but it doesn't stop. It gets noisier and noisier until it sounds like the water is boiling furiously and it will explode. Last night I was wakened at 3.30am with what sounded liked a dull 'whoomph' and a small amount of water leaking from what looks like some kind of pressure release pipe.

This interferes massively with my sleep pattern! I either have to try stay awake after 11.45pm until I think the water is hot enough or get up early enough to switch it on to get it hot enough for the day before it goes off at 8.45am. I had a plumber in yesterday doing something else and asked him to look at it. He wasn't familiar with the meter set-up but checked the two immersions. The boost one was set at 60c which he said was fine. The main one was set at 70c which he turned down to 60c. The water still boiled through the night though. What is missing / not working here to cause the water to boil? I can't believe I have to stay up during the night to take advantage of white meter water heating!

Thank you in advance!

The thermostat is kaput (that is what he turned down). Surprised the plumber did not realise, he was obviously an idiot. A replacement is only a few pounds and should only take a few minutes to fit, no need to drain down or anything.

Find another plumber or even a sparks.

Cheers winston1! I did wonder if it was as simple as that. I'll get a different plumber to come and have a look at it.

A new thermostat will have an overtemp trip on it too, preventing boiling if the thermostat fails

You need a new "resettable" thermostat, you will notice the small reset hole this is because with non resettable type if the thermostat on one immersion heater fails it can cause both the over temperature cut outs inside the thermostats to open, so you have to then replace both the good one and bad one. So make sure the cut out is resettable.

I would go so far as to say the plumber is a dangerous idiot.

There has been at least one case of a person being killed as a result of a faulty thermostat boiling the water.

As a result the new thermostats, with overheat protection, are now used.

It was a very distressing case and I'd expect any British plumber or electrician to know about it, to take it very seriously, and to fit a new modern thermostat.

If the one you called works for a company, complain to them.

He is not competent to practice.

very sad

https://www.theguardian.com/uk/2008/jan/08/uknews4.mainsection

http://www.telegraph.co.uk/news/uknews/1434588/Woman-killed-by-boiling-water-pouring-on-to-bed.html

Died for want of a £10 thermostat.

There are two types of header tank, the thermoplastic type will fail with boiling water, there is however a plastic tank designed for use with back boilers and other solid fuel water heaters and of course the steel tanks which can take boiling water, of course you still don't want the water to boil, but with some header tanks it will do no harm.

The cut out can be built into the thermostat or a separate unit this shows the separate unit, already shown built in type, the unit shown is not a thermostat it is a cut out for when the thermostat fails.

Since we don't know what type of header tank is fitted in your house, it is wrong to criticise the plumber too much, however clearly the thermostat was faulty and although turning it down may have caused it to temporary work again, he should have advised it needs renewing. The off peak thermostat will normally be set higher than the boost one, so if in error you leave both on then the boost will still only activate when water is drawn assuming good insulation on the tank.

ericmark said:

Since we don't know what type of header tank is fitted in your house, it is wrong to criticise the plumber too much

Click to expand...

No it isn't.

Postulate a plumber who says "I've looked at your tank and it's a galvanised iron one, so it's OK to have your cylinder boiling and spurting boiling water and steam into the loft while wasting 50p worth of electricity an hour. Most likely it won't kill you by drenching you in boiling water so that's OK. If the plastic overflow pipe melts, or a joint gives way, or someone walking past the building is scalded, that's just an unfortunate accident"

ceres said:

a dull 'whoomph' and a small amount of water leaking from what looks like some kind of pressure release pipe.

Click to expand...

Unvented cylinder?

There is a competance test for plumbers, show them a selection of pipe clips and ask them what they are, 90% will say "no idea"

I find those reports of people scalded to death very distressing.

Thanks for everyone's comments. It's very helpful for someone who's not knowledgeable and has to take what a tradesman says at face value. To be fair, this is a large well-respected local company who've done many jobs for me before in a different property and I've never previously had any problems.



This is what the cylinder looks like - apologies for the orientation, can't find a way to rotate it. The rusty staining on the cylinder jacket is old and pre-dates my arrival. The pipe which leaked a tiny amount last night is the white plastic at the left - there was a tiny bit of wet at the joint about a foot above floor level and a little damp where I've stuffed the kitchen towel at the skirting board.

I've got an electrician coming tomorrow to (hopefully) sort it out and now I know from the responses above what I should be looking for. Thank you!

Update: the electrician has been and fitted a new thermostat - exactly the same as in ericmark's post #5.

Thanks everyone, hoping for a full night's sleep tonight!