Electric immersion heater?


Postby jlc » Mon Aug 06, 2012 11:38 am

Hi

Moved into a new house a few months ago - central heating system is slightly different from previous house and I'm wondering if anyone can help explain what's going on

Downstairs we have the normal boiler, timer & thermostat. In the airing cupboard though, where the hot water tank is, there seems to be some additional electric control box which switches the electric immersion on and off (it's a British Gas installation if that helps explain it?) In our previous house there was a switch to turn the immersion heater on when we needed to top up the hot water. But here there is no manual control and instead there's some sort of automatic switch which comes on whether we want it to or not

Often, once the timer has knocked off and the boiler shut down this immersion heater seems to carry on heating the water. The thing is that sometimes if I wake in the night it's still going, even if it's 2 or 3 in the morning. I can't seem to override it or set it anywhere, it seems fully automatic. And now I've just got a huge electricity bill, double what it was in the previous house even though our consumption is the same

There is a switch near the box that seems to control this electric immersion and today I tried turning it off. Problem was that it is obviously wired in some way to the downstairs timer because that went off too, meaning there was nothing to trigger the boiler.

Seems like a stupid installation to me because all you really need is a manual switch to turn the immersion on and off. Is it likely to be complicated to do this? And can anyone tell me a good place to search for a reliable heating engineer? (I'm in London SE12)

Thanks a lot
John
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Postby plumbbob » Tue Aug 07, 2012 4:39 pm

By your description it seems the immersion is linked to the an Economy Seven system. The automatic timer is there to switch the heater on at midnight and off again at eight in the morning. If everything is working properly, it should be quite efficient as far as cost goes and it wouldn't be normal to have noticeably higher electricity bills because of this.

Depending on the boiler efficiency, it can be cheaper to heat the water in the summer by immersion than by a traditional gas boiler.

Of course, if the timer is incorrectly set or faulty, than this may explain the problem.

There must be a way of isolating the immersion. Can you upload a picture of the controller?

Can you confirm you have a two rate electricity meter?
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Postby jlc » Sun Aug 26, 2012 12:32 pm

Hi Plumbob

Thanks for your response - sorry for the late reply...

Here are some pics of system in the airing cupboard. I've no idea what the big blue box is as I don't remember anything like that in the system at our last place

We are definitely NOT on economy 7 and the elec meter is a single rate meter so I'm baffled about why it's running in the late evening/night

Cheers
John
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Postby plumbbob » Sun Aug 26, 2012 7:49 pm

That blue box has nothing to do with an immersion heater. It is the wiring centre for the central heating. I can tell that because the pump and motorised valve is linked to it. Almost all traditional heating systems will have one of these although to be honest, I can't remember seeing a blue one before.

So that begs the question, how do you know the immersion is switched on? What is making the noise? Is it the pump that is running? Actually, I can't even see any part of an immersion heater.
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Postby jlc » Mon Aug 27, 2012 9:44 am

Well maybe it's the pump that's running? But why would the pump be running hours after the boiler and the timer have gone off?

Also just wondering - isn't the pump solely for the central heating system? Does the pump have anything to do with the hot water supply?

Sorry if these are really obvious questions...

Cheers
j
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Postby plumbbob » Mon Aug 27, 2012 4:06 pm

jlc wrote:Also just wondering - isn't the pump solely for the central heating system? Does the pump have anything to do with the hot water supply?


No. You have a "Y" plan system where both the hot water and central heating systems are pumped. This is by far the most common type of arrangement (pre the modern combi boiler that is). If you want to see a diagram of your system, Google for "Honeywell Sundial "Y" plan diagram".


jlc wrote: But why would the pump be running hours after the boiler and the timer have gone off?


It actually isn't the timer or thermostat that directly controls the pump. Depending on the type of boiler you have, the pump is powered from either the boiler or the motorised zone valve. It is not unusual for the pump to continue for a short while after the boiler has closed down. This is referred to as "pump overrun" and is required to protect the heat exchanger. It might be expected to run for up to 20 minutes so if yours is still running in the night it could be a faulty boiler circuit board. If the zone valve controls the pump, then it may be faulty and not returning to rest after the timer is off.

What we need now is the boiler model and for you to test the operation of the zone valve.
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Postby jlc » Wed Aug 29, 2012 1:36 pm

It might be expected to run for up to 20 minutes so if yours is still running in the night it could be a faulty boiler circuit board


I think this might be it. Last night the boiler went off at 8.00 but the pump was still running at 9.30. Went to look at the boiler and the red light was flashing signalling "lockout". Pressed the reset button on the boiler and the pump switched off straight away, which suggests it's the boiler that's the problem

What we need now is the boiler model


The boiler is a Potterton Suprima 50L. It's ten years old (I checked the serial number)

Actually I've had this 'lockout' problem a lot and have to use the reset button regularly. A google search came up with loads of people with the same problem - getting lockout on the boiler and having to reset. Seems its a problem with this particular boiler and often it turns out to be the circuit board

Looking around it seems like it would be about £ 300 to get a new one fitted. Is it worth it with a ten-year old boiler?

and for you to test the operation of the zone valve


How do I do this?
jlc
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Postby plumbbob » Wed Aug 29, 2012 9:44 pm

jlc wrote:Looking around it seems like it would be about £ 300 to get a new one fitted. Is it worth it with a ten-year old boiler?


Well, that's the sixty four million dollar question isn't it? Maybe you should look at upgrading your heating system entirely with a new combi boiler but of course that will cost a lot more than a new pcb.

The motorised valve has a lever on the side or end which when pushed firmly will operate the valve manually. You should be able to feel and hear the gears revolving.

It won't be the valve at fault though, as the pump on your system is controlled by the boiler.
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