Immersion Heater Stat Keeps Tripping

[old wrinkly]

I recently had a new Gledhill EnviroFoam SE42X16IND Hot Water Cylinder installed. In accordance with the instructions with the tank I also had a new Euralloy 27 inch immersion heater & stat fitted, manufactured by Tesla(UK) Ltd of Birmingham.

As I am currently on Economy 7 for electric (I am reviewing this as my figures, provisionally confirmed by NPower, suggest it may not be the best option despite using 26% of my electric on night rate) I was running the immersion via a Greenbrook T!05-C 7 day digital timer with two "On" periods, one for 4 hours during night rate and the other for 3 hours during the evening (day rate) to cater for showering.

At first everything seemed OK but then after 4 days I found that the stat had tripped out so no hot water. Spoke to the retailer who told me to just press the reset and everything would be fine from then on (they seemed aware of some issues of this nature). Did as asked and started working again but then approx every 4 days the stat would trip out. Usually I would find this out in the morning.

Spoke to retailer again and they suggested taking a replacement immersion heater and stat. Replaced the stat as a first step with a new Backermatic but problem still persisted. The Backermatic is preset to 60C and has a silicon blob to prevent adjustment of the temperature.

Although I had changed the stat I contacted Tesla as I had the problem on both makes of stat and their immersion heater was still fitted and they told me the problem was easily solved. They said the stat was detecting the ambient temperature in the airing cupboard and when this reached 70 (didn't specify C or F) it would trip. This was in accordance with EN 60335-2-73.

Told me to cut a 12 inch square hole in the ceiling of the airing cupboard to vent to the loft and fit a standard grill on the bottom of the door to provide air flow. As a test before doing this they said to run the system with the airing cupboard door left slightly open.

Ran with the door open but problem still existed. Contacted Tesla again to ask if there were any other circumstances when the stat would trip out but no answer as yet.

On Sunday I removed the Greenbrook timer and fitted a straight on/off switch with neon to see if this made any difference and I left the power permanently on. Thought this might show if it was the timer at fault but also wondered if the switching rates over night might be a cause as the stat had usually failed over night.

This morning the stat had tripped out again so only ran 2 days this time.

Have looked again at the instructions with the Tesla stat and although it says the stat will trip if the water temperature exceeds 97 degrees Celcius there is nothing about the ambient temperature.

At the suggestion of a friend I have now switched the immersion power on again and placed a temperature gauge in the cupboard. The door is still partially open but within an hour the temperature recorded 81.7F(27.6C) and still seems to be rising.

My property was built approx 1960 and the airing cupboard has no venting.

Wonder if anyone has come across this and can offer any advice as I am completely baffled. Don't want to start hacking away at the ceiling or fitting the new immersion heater without some evidence this will cure the problem.

Thanks in anticipation.

 

[kme]

OK.

There are TWO seperate "stats" involved here; or at least one with two distinct functions (one may, or may not, be part of the immersion unit.)

One is the "satisfied" water temp; which switches in and out to control the immersion itself - should be set around 60 deg. C. This type does not "trip", it simply stops the immersion constantly boiling the tank (think of the OLD kettles, which had to be switched off manually, against the "automatic" ones that shut off at a given temp.)

The second stat is a safety device; designed to "trip" if the standard thermostat fails, and the immersion tries to overheat the water - it shouldn`t trip out unless the WATER gets too hot - and the airing cupboard temp should have little bearing, TBH.

So there are, IMO, three options.

1. The wiring is wrong to the immersion - hasn`t been taken through the integral stat.

2. The water stat is set HIGHER than the overheat stat (or maybe very near the same temp?)

3. you`ve got a faulty water stat (either of `em).

HTH

KME

 

[SPECIAL LOCATION]

+1....

IF ambient temperature IS a problem (rather than water temp)..

Spose as a bogit & fixer solution an external bog-standard room thermostat..

and a contactor could diss the power to the Imm heater?

:C

 

[old wrinkly]

hanks for the reply.

1) I wired the thermostat myself in accordance with the wiring diagram provided by Tesla. My plumber will not deal with any electrical wiring.

Not rocket science, neutral to neutral terminal of immersion, earth to earth of immersion and live in to one side of the thermostat and live out to the live terminal of the immersion.

All wiring double checked and confirmed correct.

2) Thermostat temperature on the new Backermatic is as stated preset to 60C and cannot be altered without removing the silicon blob which invalidates the warranty.

3) One I can accept but two, of different makes seems very unlikely. However, is it possible for 2 separate makes of stat to be so widely off the mark that the temperature setting can't be heeded.

The normal "satisfied" water temperature stat is working OK. I have a energy monitor meter which shows Kwh being used and this clearly shows when the water is being heated and when it's not. Also when the safety trip kicks in there is mains power to the live in of the thermostat but no power to the live immersion terminal. As soon as it's reset power is restored to the immersion live terminal.

As explained by Tesla the safety trip is part of EN 60335-2-73 to avoid accidents when the immersion goes open circuit.

Interesting to read your comment about the airing cupboard temperature as I was not fully convinced about the explanation given by Tesla, especially after reading the wiring instructions a couple of times, but they are the experts!!!

Under what other circumstances could the safety trip be activated?? Could a faulty immersion element be the issue? As far as I can tell there is no separate "stat" on the immersion element itself, the safety stat is only part of the normal stat which is housed in a sleeve and not touching the water itself.

Even wondered if the electic meter switching rates might be causing a spike, but dismissed this a highly unlikely as nothing else is affected.

 

[kme]

What is the model of thermostat / immersion please? Think this needs a bit more dissection, as something isn`t right!

edit: can you post a photo of it??

 

[NozSpark]

I had a similar problem (boiling sounds), what I figured out was happening - as the temperature was approaching 60deg the element was boiling the water near it, in my case it didn't trip the over temp but it did make a boiling sound..

Never did sort it properly in the end,,, but maybe it's too many "amps per inch" as someone once said (regarding NSH elements)??

 

[old wrinkly]

Thanks for the replies.

As stated previously the immersion heater and stat are both manufactured by Tesla (UK) Ltd. The immersion is Euralloy Titanium 3KW 27inch and the stat is I think model TS230.

After searching with Google found numerous forum posts where people are having exactly the same problem. In many cases people have done multiple changes of the immersion heater &/or thermostat but the success rate isn't exactly encouraging.

I am due to visit friends for a few days later this week don't have much time to make much more investigation .

However, after reading all the posts there does seem a case for thinking there are issues with the safety trip or the immersion stat not reading the temperature correctly. This could give rise to the situation where although set to 60C the "satisfied" water stat the actual water temperature is mugh higher. Likewise, if the safety trip is set to trip at 90C but is in fact tripping at a lower temperature then if the water temperature is higher then the safety trip could be activated earlier then necessary.

As a short term test I have reinstalled the original Tesla thermostat as this doesn't have the silicon blob and can therefore be adjusted and I have set this to 50C and left mains power on.

I can then test whether the temperature of the water is OK for normal use and also see if the safety trip is activated as before with the stat set lower. In theory with a lower stat setting the water temperature should not get anywhere near the safety trip setting of 90C.

I am now convinced that the theory given by Tesla that it is being triggered by the ambient temperature in the airing cupboard is inplausible because I cannot see how any device enclosed within the cap of the immersion heater which gets quite hot could possible detect any temperature outside of the cap. Also, despite a detailed search I can find no evidence anywhere that the ambient temperature, which is around 26-28C, affects the stat in anyway.

I assume there must be an industry standard for the tolerance of both the "satisfied" water thermostat and especially the safety trip but don't know what these are. If anyone can help would be obliged.

I will report back on how I get on with the new settings in due course.

 

[kme]

I think that, in your position; and knowing of the issues with this particular kit - I`d replace the whole thing with a different make, and send the Tesla back for refund ("unfit for purpose" being the legal term necessary)

KME

 

[Apache]

As I am currently on Economy 7 for electric (I am reviewing this as my figures, provisionally confirmed by NPower, suggest it may not be the best option despite using 26% of my electric on night rate) I was running the immersion via a Greenbrook T!05-C 7 day digital timer with two "On" periods, one for 4 hours during night rate and the other for 3 hours during the evening (day rate) to cater for showering.

I wouldn't tolerate this in a new set up. How many people live in the house? If you need the immersion on in the day then you don't have a big enough tank. We are 2 adults and we can have 4 showers in a day and still have hot water spare, just leaving the tank on permanently on the eco 7 (210 l tank).

Think it's time to get a professional in who understands these things. Something not right here.

 

[old wrinkly]

Thanks for the replies.

KME

I have a ThermTec Ltd AFSZB-367 immersion heater and a 11 inch Backermatic BMST11 thermostat supplied by the retailer as a replacement if I decide to go that route. Have kept retailer in the loop and they are happy to go along with whatever I decide even if it takes a couple of weeks or more.

Is your comment on returning the Tesla based just on my posting or have you come across similar problems with the product in the past?

Apache

Immersion is on all the time just to see if the safety trip activates. Was previously only running it periodically, see my original post.

As for the tank, the one I have was the maximum size Gledhill I could fit in my airing cupboard and is approximately the same capacity as the old copper one (114-116 litres) which was more than 25 years old.

There is only my wife and I and we generally only have 2 showers per day and use little hot water in between. Not really had any problems with lack of hot water in the past.

. If we go away from Economy 7 which by figures is costing me around

 

[kme]

I`ve not had direct dealings with the Gledhill tanks for some time - at the end of the day, a (vented) tank is a tank is a tank - if it doesn`t leak, its OK!

I`ve seen but not fitted the Tesla stuff - I was going by your reference to known issues. If other people have had similar problems, the kit had an inherent design fault - send it back.

Backerman stuff is, in my experience, good kit that does what it says on the tin - immersion with stat & o.heat stat isn`t complex kit - irrespective of the cylinder its attached to.

KME

 

[batty]

Is there plenty of air around immersion top?

 

[old wrinkly]

Yes the immersion top is clear of any obstructions and has nothing immediately above it, the shelving is cut back

Initial tests with the lower stat temperature setting suggest this may be the issue as it ran for 4 days with tripping out. I am away for a few days now so will have to see what happens when I get back.

 

[nsbs]

Does the tank have 1 or 2 elements in it. i.e one at the top and one in the middle.

 

[old wrinkly]

Hi, as previously stated there is only one immersion element which is at the top.

Since coming back from my break it looks as if setting the stat down to 45 degrees instead of 60 has settled things down as it has now been running for 5 days without tripping plus the 4 days before I went away. The water is still hot enough for everyday use.

I have not had any further correspondence from Tesla since telling them that their suggestion to do a test run with the airing cupboard door open hadn't worked.

It is now my firm believe that my problem was nothing to do with the ambient temperature in the airing cupboard and can't think why this was ever suggested, perhaps that is why Tesla have gone quiet.

Still can't work out why 2 different makes of stat should exhibit the same problem but provided the system keeps working I can live with that.

 

[Alan Bayley]

I have just had a new bathroom fitted with a power shower and new hot water cylinder, immersion heater element and thermostat. My cylinder stat also trips the over heat button on the thermostat and needs resetting.

I have had three new thermostats fitted and the problem still persists. The problem has to be that the over heat trip is measuring over 90 deg C. I have even changed the programmer. Setting the water temperature at below 60 deg. is a risky business because you run the risk of allowing bacteria to grow in the hot water cylinder. The most likely cause of the tripping in my opinion is that water is leaving the cylinder faster than the cylinder can refill which is causing some air bubbles to form at the top of the cylinder and allowing the immersion heater element to get too hot at the top where the trip sensor is positioned. These thermostats are very simple

bi-metallic devices and are not susceptible to electrical interference.

Hopefully the solution may be as simple as fitting a thermostat and element made by the same manufacturer. Unfortunately I believe the problem is going to be cavitation in the top of the hot water cylinder and heaven only knows what the solution to that is. When the company who fitted the bathroom fix the problem I will post the solution.

 

[old wrinkly]

Hi, thanks for the input

Keep posting what the company who fitted your bathroom come up with.

Have now been running the system at around 45C for close to3 weeks and no tripping out. As regards bacteria, I am not convinced as yet that the lower temperature setting will be an issue but then who knows. A quick test with a jam thermometer held under the hot water tap suggests the actual temperature is close to 60C not the 45C setting.

 

[Adrian41uk]

........ The most likely cause of the tripping in my opinion is that water is leaving the cylinder faster than the cylinder can refill which is causing some air bubbles to form at the top of the cylinder and allowing the immersion heater element to get too hot at the top where the trip sensor is positioned.....

I don't see how this can happen. The cylinder is supplied by a cold water feed towards the bottom of the cylinder & the hot water leaves from the top. Also connected to the top is the open expansion pipe. If the hot water were drawn off at a rate faster than the system can replenish it with cold then the water level falls in the expansion pipe, being replaced by air, and the flow rate reduces. I cant see how this air can enter the cylinder. Even if the cold water feed is cut off altogether then hot water pipe will empty but the cylinder will remain full.......

Adrian

 

[old wrinkly]

Hi, been following the follow up posts.

I have assumed that the safety trip is linked to the normal stat i.e it detects the water temperature in the same way as the usual stat. Is this correct, or is the safety trip a separate sensor in the head of the thermostat??

 

[batty]

Generally I think the feed goes through over heat first then into stat that way if water gets to hot overheat pops out stopping supply.