Immersion heater thermostat keeps tripping.

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Got a Redfyre oil fired boiler for central heating and hot water and use immersion occasionally. The boiler has a rotary varying thermostat low-medium-high. I run the thermostat at just above low. There are no other thermostats in the house apart from the themrostat physically on the immersion element.

I live in soft water area.

The hot water cylinder is vented and there are no blockages.

I fitted a new Horstmann electronic timer 5 years ago that has a boost function that I like to use a fair bit.

Recently replaced hot water cylinder and immersion. Original approximately 25 years old and don't think immersion was ever replaced. Replaced water cylinder like for like as far as possible but new immersion, (will find make and lenth and advise) has new reset function (unfortunately). One thing that is different is that the new cylinder top is flat and the original had a domed shape top to it. This means that the immersion heater housing sits just that little bit closer (approx 2" closer) to some stored towels on a rack which now sit approximately 5" above. The tank lagging (not foam but is a like a more traditional fibre type with a plastic polythene type outer) does not cover the immersion heater housing.

Problem is that I have to reset immersion every one to two days.

Wiring is fine, clean and secure and no shorts although I am using 2.5mm butyl cable. Should I perhaps use ordinary twin and earth as recently a plumber advised that he doesn't see butyl used much these days?

One thing I did notice that on offering immersion into cylinder, not a great deal of lateral movement of immersion would result in immersion touching the central heating coil. Presumably the immersion should fit inside the central heating coil without any problem? Or should the immersion heater lowest siteing point be a minimum distance above that area?

Also, when unpacking immersion, I noticed half-way down the shaft of the immersion was a red plastic securing-clip/seperator that I thought perhaps stopped the thermostat and heating element clattering together perhaps during transit. I threw this bit away before fitting the immersion. I was worried the thing would break off at some point, float to the top of the water and then block a pipe. Should I have perhaps left this thing on? Is the function of this item to perhaps keep the distance between the heating element and thermostat static? In which case, oops!

I don't as yet want to go down the line of replacing immersion or therostat until I have ruled out any other possible causes as I've read that too many people do this (sometimes 3-4 times) to no avail.

Is it perhaps just a simple case of the new immerions with the reset button don't like old redfyre oil fired boilers and trip as a passtime as a result? I have set the boiler to its lowest setting whereby any lower and the house does not get warm enough on freezing days and the problem still occurs.

As yet, I haven't had a day over this winter period where I haven't used the boiler purely relying on the immersion for just hot water so I can't as yet rule out that the boiler heats the water too much to result in the immersion heater tripping.

I have set the immerision heater to max and at 60 degress and the same occurs although if the boiler is overheating the water to the extent that the immersion needs resetting, I can't see that the temperature setting on the thermostat would make much difference.. I will try turning the power off to the immersion permanently whilst using the boiler for central and hot water and see if the reset button trips. Presumably the immersion and thermostat doesn't need to be energised in order for the reset button to trip?? Surely it's just a passive device??

Lastly, the supply voltage in my village does get as high as 255vac and we have power-cuts at least every 10 days and sometimes 2-3 times a week..Could this cause a problem??

I have a temperature probe on my spangley new multimeter. I don't know how accurate these things are but will check the temperature of the hot water and advise results asap.

Finally, hurrah, the cable for immersion is just long enough from the controller to the immersion housing. It is not stretched however is slightly tight because the new cylinder was that bit taller. It gets slightly warm to touch when it's in use but then I would expect it to a certain extent given that it must draw 15 amps or slightly more as I can't remmeber the exact power rating of the immersion itself. Should the cable itself be longer and slacker and should I perhaps be using 4mm twin and earth anyhow instead of being a tight and reusing the butyl that I fitted when I installed a Horstmann electronic timer 5 years back??

Any help please I would be most grateful... Thanks Rob.

Right, I'm off for a bath....
 
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So let me get this right.....

You are paying to heat the tank with electricity and paying to heat the tank with oil at the same time?

If so... Why?
 
Following a fatal accident, modern immersion heaters are required to have an overheat cutout that operates independantly of the thermostat, and requires manual intervention to reset.

These cutouts weren't fitted to older immersions.

It sounds like the boiler hot water temperature may be exceeding the operating temperature of that cutout.

What controls do you have for your water heating?
Is there a cylinder thermostat fitted to control the boiler? Is it working?
 
The only temperature control I have for the water heating and central heating is the control on the redfyre boiler which varies between low
and high. There are no other thermostats in the house. It is curently set to low which heats the house nicely to around 21 degrees. As the hot water system is gravity fed, I can have hot water alone or central heating including hot water.

Lastly, xr4x4, no I don't use them both together. Which makes me think that the thermostat is a passive device. I like to cut the immersion in for an hour between 5-6am as sometimes after a late night bath there isn't enough for the following morning having turned the boiler central heating and hot water off say at 9pm the previous night.
 
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Just measured the hot water temp with multimeter test probe after having the heating on for most of today and it measures consistently at 58 degress c. As mentioned before, I don't know how accurate these things are?
 
Immersion cutouts should only operate when the water gets to 90C or similar. Therefore either the water is getting that hot at some point, or the new immersion thermostat is faulty.
As you have gravity hot water, it is likely the water is being overheated.

The cutout will work regardless of whether power is connected.
Supply voltage and power cuts won't make any difference.

Twin and earth is totally unsuitable for connecting to an immersion heater - don't use it. The butyl cable you have is fine.
The immersion thermostat should normally be set to 60.

As well as heating water electrically which will cost far more than any other fuel, why have you had a new cylinder fitted, and yet not had the system converted to fully pumped with the appropriate thermostats and other controls?
Everything you have described so far just ensures your heating and hot water costs as much as possible to run!
 
have an overheat cutout that operates independantly of the thermostat, and requires manual intervention to reset.

These cutouts weren't fitted to older immersions.

There are 2 types os cylinder 'stats on the market since the new legislation.
One without the secondary cut-out (old style) and one with.
These have them, the little-red-thing to the right of the big-red-thing-with-the-blob-of-silicone-on:
BMST11-BMST18-BMST17.JPG
 
You said so much in your first post but NOT the vital information I need to make any judgement!

What temp is the thermostat set at? It should be set between 50-60 C.

Many are rather oversensitive and nuisence tripping is common if its set to 60 or higher.

You need to work out if its tripping during electric heating or when the boiler is on.

You should stop using expensive electric heating and set your boiler to heat the water say 20 minutes before the CH.

You have a very antiquated system and should upgrade the controls to give you proper thermostatically controlled CH and HW. That should pay for itself within one year!

Tony
 
Hi Agile, as mentioned in my first post, I have previously set the thermostat to max and at 60 degrees and the same problem occurs. The immersion thermostat is currently set to 60 degress.

Out of interest, I've just measured the hot water temp again this time at a bathroom tap all of 18" away from the cylinder and the temp measured at 61 degress c.

When the weather improves, I will run the immersion on its own for a few days and let you know how I get on.

Yes it is pretty antiquated here! This year will see some sorting out in the house for a change rather than the roofs and drainage. We'll get there!

Hi Charnwood. Yes the immersion stat I have has the small reset button.


Hi Flameport. The hottest hot water measurement I have taken so far is 61 degress c. Assuming for the moment that the cut-off on the immersion is healthy, could it be effected by the heat coming away from the central heating coil in the cylinder? When the weather improves I will experiment with keeping the central heating off and just running hot water via the boiler to see if the cut-off on the immersion trips out.

I'll stick to the Butyl then. I did wonder about the twin and earth as I have seen a few immersions in the past where the terminals had run loose where twin and earth had been used and some terminals have been burnt. I've always used Burtyl when wiring in a timer in the past.

"As well as heating water electrically which will cost far more than any other fuel, why have you had a new cylinder fitted, and yet not had the system converted to fully pumped with the appropriate thermostats and other controls? Everything you have described so far just ensures your heating and hot water costs as much as possible to run!"

Fair comments mate. Stupidly perhaps, It was purely a case of it works so I'll leave it alone! That was until the tank sprang a leak and busted the foam insulation lagging. Needed the system working asap so a plumber mate who owed me a few favours found a new tank and immersion for a ton fifty and installed it for me for a couple of pints one evening. Can I still easily modify the system to have the hot water fully pumped with all the appropraite controls at a later date? Just looked at my bills and oil for a year is costing £620 which lasts me between Nov and mid-March as a rule for 1000 litres. The immersion costs in round figures £0.14/Kwh inc VAT x rating so presuming a rating of 3Kw that I need to check, (don't know where I originally got 15 amps draw from but nevermind!), it would cost around £56.70 for an hours use a day for four and a bit months. For the rest of the year (7 and a bit months for three hours a day) It works out at £283.50. So to provide heat and hot water for this 4 bed detached costs roughly £960. Discounting any central heating pump costs.

Roughly speaking Flameport, percentage-wise, how much do you think I could save with pumping the hot-water and having a proper upstairs and downstairs roomstats fitted? The temperature over the house is pretty consistent between 20-21 degrees with the central heating on.
 
Impossible to say what the savings are, but as a very rough estimate you should be able to save at least £200 per year, and probably more.

Installation would just be a couple of motorised valves, some fairly simple alterations to the pipes, a cylinder thermostat, one or more room thermostats and some fairly simple control wiring.

The advantages wiil be:
a. You won't need the electric immersion heater at all, and although the price of oil varies considerably, it will still be cheaper than electricity. (You should still keep the immersion in case of boiler failure).
b. The boiler won't be continuously heating the hot water while it's on - water will only be heated when required.
c. You can turn the boiler thermostat up to maximum, which will mean your hot water cylinder will heat up in a fraction of the time it takes now, and your central heating will heat your house to the desired temperature far more quickly.
d. You can actually set the room temperature you want, and the boiler will switch off completely when this temperature is reached. (obviously switching on again when the house cools)
e. If you have 2 room thermostats, you can have the bedrooms heated to a lower temperature than the other rooms, and/or programmable ones can have different temperatures at different times of the day. Both of which will reduce your heating costs.
f. If the problem with the immersion is due to the boiler overheating the cylinder, this won't be a problem any more.
 

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