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Author: ajr5263 One star, 50 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: of 69816  
Subject: Immersion Heater Thermostat problem Date: 18/01/2009 18:36
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Hi everyone

I have a problem with the Immersion Heater in the property I rent out, and I'm going round and round in circles on it, so I'm hoping someone here will understand these things better than I do.

The story so far:

Property is a ground-floor flat with an immersion heater in a large hot water cylinder. The property has Economy 7 electricity and so it has an electronic time controller to control when the hot water comes on. It's got a dual-element setup, where you can choose element A (overnight heat) or B (quick boost) to come on.

Recently, the time controller failed such that it lost the current program and time every night. The whole setup is about 12 years old, so I figured it would be easiest to just replace the controller. I called in an electrician and he replaced the controller. The only catch is that he described the existing controller as a combined controller and thermostat - it also had a thermostat connection into the tank that regulated the temperature as well as controlling the time. The new controller fitted did not do this, so he fitted a separate thermostat to the element.

Now, the new controller works fine in terms of timing, but the new thermostat has a problem - the water simply doesn't get hot enough. The electrician has been back several times to change the thermostat, and he's convinced that the thermostat works properly (having tested it in another system). He said that new regulations mean that the maximum temperature you can set the thermostat to is 60 degrees Celsius. However, even after being on for 5 hours overnight, the water temperature is just over 40 degrees, so it's not getting anywhere near that level, despite the thermostat being set to 60 degrees.

The tenant isn't happy, since this means you only get one lukewarm shower before you need to boost it, and it's certainly not working as well as it did before the controller got changed. I find it hard to believe that 40 degrees is an acceptable temperature for a hot water system, but the electrician has basically declared this is as much as he can do.

Does anyone have any suggestions? My suspicion is that the element is somehow incompatible with the type of thermostat he's using, but I don't have much detailed knowledge about immersion heaters.

Thanks for reading this post, and any suggestions you can give.
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Author: JonEBehr Big gold star, 5000 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 60658 of 69816
Subject: Re: Immersion Heater Thermostat problem Date: 18/01/2009 19:37
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It's got a dual-element setup, where you can choose element A (overnight heat) or B (quick boost) to come on.

I've only ever seen a setup with an immersion heater near the foot of the cylinder to heat the whole lot on the economy7 supply and a smaller one near the top to heat/top-up just the top of the cylinder on the regular supply. Each immersion heater had its own integrated thermostat as controlling either by just a thermostat stuck on some arbitrary point on the cylinder wouldn't make much sense (though I'd expect over-heat rather than under-heat on the top-up). One could cause the overnight to run to max temp but have the top-up thermostat set a bit lower if you didn't need max temp later in the day.

Did he explain why he didn't replace the old control-box with one of equivalent functionality?

Cheers!

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Author: Mike4 Big gold star, 5000 posts Top Favorite Fools Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 60660 of 69816
Subject: Re: Immersion Heater Thermostat problem Date: 18/01/2009 21:15
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The only catch is that he described the existing controller as a combined controller and thermostat - it also had a thermostat connection into the tank that regulated the temperature as well as controlling the time.


Verrrry Interesting! I've never seen such a set-up in my career as a plumber (except on the very latest generation of high-tech thermal stores, less than about three years old). NOT to say he is wrong, of course!

The whole story does not stack up. Even if the stat turned OFF at 40 degrees there would be a whole tank of water at 40 degrees - enough for 10 to 15 minutes of showering with a decent performance shower. 40 degrees is STILL a little hot for comfort in a shower. Further, all the immersion heater stats I fit are calibrated up to 73 degrees C and I know nothing of a reg limiting temps to 60 degrees C.

My suggestion is get a competent heating technician in. My view is this bloke is blagging you. The thermostat appears not to be heating the water to 60 degrees and I don't think he knows what to do about it.

It could be that the tank is heating perfectly and its a shower mixer problem. How do you know the hot water is only heating to 40 degrees overnight? Has someone measured it using a thermometer under a hot tap first thing in the morning?

Cheers!
M4

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Author: ajr5263 One star, 50 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 60662 of 69816
Subject: Re: Immersion Heater Thermostat problem Date: 18/01/2009 22:00
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Hi M4

Many thanks for your response.

How do you know the hot water is only heating to 40 degrees overnight? Has someone measured it using a thermometer under a hot tap first thing in the morning?

That's exactly what I did to get that temperature measurement. My tenant reports that the first shower is fine, but after that you're basically out of hot water and need to boost it (at daytime electricity rates).

Whereas before this change happened, the water was significantly hotter (I didn't measure it, but I'd guess at least 60 degrees, since it was hand-hot from the hot tap first thing in the morning), so the first shower didn't cool it to the point where you noticed it getting cold. I don't think it's an issue with the shower, since the temperature from the hot tap is also significantly lower first thing in the morning.

The old controller was a Pactrol Micro 7 Plus (long since obsolete). The data sheet can be found at http://www.pactrol.com/pdfs/Micro7.pdf. It's about 12 years old. Having re-read the instructions at that link, there's no mention of it containing any kind of thermostat so I'm starting to doubt this also.

How would you suggest finding a suitable person to look at it? I found this guy as an NICEIC approved domestic installer (found him through their website). Is there a different qualification I should be looking for?

Many thanks once again

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Author: Mike4 Big gold star, 5000 posts Top Favorite Fools Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 60663 of 69816
Subject: Re: Immersion Heater Thermostat problem Date: 18/01/2009 23:15
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That's exactly what I did to get that temperature measurement. My tenant reports that the first shower is fine, but after that you're basically out of hot water and need to boost it (at daytime electricity rates).

Right, in that case he's probably having a ten minute shower at ten litres a minute!

It sounds to me as though the electrician as well as fitting a new timer, has fitted a new thermostat in the off-peak immersion heater and it isn't working correctly. These are blindingly easy to replace if necessary but first, I suggest taking the plastic cap off the heater element (power OFF first) and reading the temp setting on the thermostat dial. It will be adjustable with a small screwdriver. If it can be turned to a higher setting, do so! If it is already at MAX, then a new one should sort it out.

Another possibility is that the new timer has not been configured correctly, and is only heating the tank for a very short time. Have you checked its time switching settings?

I don't think you should be using an electrician. A plumber is a better bet. A plumber with some electrical knowledge. Interview a few on the phone and select one who seems to understand the concept of off-peak electricity supply ;-)

Cheers!
M4

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Author: ajr5263 One star, 50 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 60967 of 69816
Subject: Re: Immersion Heater Thermostat problem Date: 01/03/2009 14:47
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In case anyone stumbles across this thread in future, I thought I'd post the eventual outcome of this.

We were all looking in the wrong place for the problem. The new time switch and thermostat were functioning just fine. The problem was a plumbing one. There is a three-way thermostatic valve next to the immersion tank that is designed to mix cold water with the hot in case the water in the tank is too hot. It appears that this had failed, and was mixing in too much cold water, thus making it appear there was a lack of hot water.

It wasn't obvious because the tank is coated in solid insulation material, and you can't actually feel the tank to see how hot the water is. When we finally got a probe into the tank to measure, we concluded it was heated to the expected 60 degrees, but this mixer valve was reducing the temperature of the water coming out below that.

The valve has been replaced with a new one, and everyone is happy. My suspicion is that the old thermostat allowed the water to get hotter, thus masking the problem. When changing the thermostat seemed to cause the problem, no-one thought to look more closely at the rest of the system - we mistakenly assumed it was related to the new thermostat.

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