Immersion Heater Stat Keeps Tripping

[old wrinkly]

Hi, follow up question. As stated by turning the stat down I have managed to prevent the constant tripping out. However, I still have an issue because the Gledhill has a top outlet that serves the main bathroom, kitchen and outside tap. This pipe is constantly hot, not a good idea to keep my hand on it too long. There is also a power shower tapping approx 9 inches from the top and this serves the ensuite (power shower, sink & bidet) and this has dip pipe that turns up in the cylinder (and should therefore always draw from the hottest part of the cylinder, this is pre manufactured by Gledhill ). By comparison the power shower tapping pipe is only warm and have had a number of times when the power shower starts hot but then runs cold even first thing in the morning when no hot water has been drawn off (the immersion is by the way permanently on). Have been speaking to Gledhill and they can't offer any reason but did say they would expect the side tapping and the top tapping to be more or less the same temperature.

As an experiment I disconnected the stat and ran the immersion for an hour and the side tapping gradually got hot and when a shower was being run it got as hot as the top tapping.

As it's well insulated I can't of course check the temperature of the cylinder at various depths as I would done with the old copper cylinder.

This rather suggests that I am not getting sufficient hot water in the cylinder for some reason when using the normal thermostat/immersion but can't think why.

Any ideas?

 

[Apache]

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

Stop pratting about and get this looked at properly.

 

[m4tty]

Bad day patch

 

[kme]

No Matty, he`s right. It sounds like there is some sort of issue here, which cannot be resolved easily. (I note we still haven`t had piccies, as requested )

Problems with DHW flow, and cold water at a mixer shower with a full tank are more likely to be poor plumbing issues, IMO - they certainly aren`t electrical!

I`ll back Adrian r.e. water flow, and air in the cylinder - that won`t / can`t happen, unless syphonage were to occur - and THAT would be a serious plumbing problem on a vented cylinder. The only air related issues are usually down to overheating the water; and small air bubbles being released from the water - which is what "surrey" flanges and the like are designed to minimise. The immersion is only ever going to be exposed to the air under two conditions:

1. The tank has ruptured, and all the water has flooded out - a bit of air around the element would be of little consequence by comparison.

2. Intentional draining of the tank - and you`d be an idiot to have the immersion on whilst doing that.

KME

 

[old wrinkly]

Can I please clarify my situation as it's obviously causing some disquiet.= wqith people thinking I don;t appreciate the advice.

The initial problem re the tripping out seems to have been cured by my turning the immersion stat down to 45C. Testing water out of the tap suggests this is still close to 60C. The tripping out issue is quite common as there are copious threads on various forums where people have experienced this and never been able to get it sorted, despite using different thermostats/immersions. General view is that the new regulations requiring the safety trip are the cause.

The current problem is as yet unresolved and my issue is that the plumber, who I have known for years, and has been in the trade for all his working life, and has done a lot of work for me has been on holiday, so it's not a question of my "pratting about" simply that I don't want to involve another plumber and besides which he is not certified to deal with electrical faults, which is how it started.

I have spoken to him briefly on his mobile and he is going to call in but as he only got back last week he is trying to catch up and as mine is not urgent he will get to me in due course. He was sceptical of the claims by Gledhill that there was back flow of cold water.

As I have said all the pipework changes was done at the cylinder end, no other new pipe exists. I sorry for missing the request for images and hopefully you will now be able to see the new cylinder and pipe work.

Last week I ran the immersion open circuit i.e I disabled the stat and after about an hour the power shower tapping started to warm up. I then turned it off and the shower was hot. Since then, the pipe has been hotter than before but whether this is my imagination I don't know. Haven't had a problem with a cool shower but this could be just luck.

 

[Alan Bayley]

I hope you are right, but one of the reason for using Surrey\Essex flanges which draw water from a few inches beneath the top of a hot water cylinders is to ensure air bubbles

are not carried through to the shower head. The new hot water cylinder which was fitted to my bathroom has a flat top to it rather than a domed end which I think could cause

small amounts of air to collect. I am not suggesting the cylinder is drawing air in but rather like the cavitation effect you get with a central heating boiler, bubbles form around the end of the immersion heater then re-condense at the top of the cylinder, so the tank doesn't fill up with air, it just maintains a small volume of bubbles at the top of the hot water cylinder while the immersion heater is on. You will know what I mean if you look at the element on an electric kettle when it is heating up, loads of bubbles stream to the surface long before the water boils. I know this all sounds very theoretical but it is an inescapable fact that 90Deg.C plus is occurring at the top of the cylinder some how, otherwise the overheat trip would not be tripping.

 

[Alan Bayley]

My plumber has now changed the immersion heater and thermostat and the problem is the same.

On inspection of the inside of the hot water cylinder the immersion heater boss is directly above the immersion heater element. The original cylinder which was discarded put the heater element at an angle within the hot water cylinder so that bubbles didn't rise directly underneath the immersion heater flange. The hot water cylinder is made by Gledhill.

Their is a fundamental design defect somewhere in the system and I don't see anybody admitting responsibility any time soon.

 

[Alan Bayley]

Six months on and I now have a hot water cylinder with an immersion heater that doesn't keep tripping the overheat stat.

The problem was pretty straightforward in the end. The Gledhill cylinder mounted the immersion heater dead vertical within the cylinder and the thread length into the boiler was too long for the immersion heater boss to protrude into the water. All the bubbles streaming off the heater element went straight up to the underside of immersion heater collected in the long threaded socket and tripped the overheat stat.

I now have a cylinder which mounts the immersion heater at 15 deg. to the vertical so all the bubbles miss the underside of the boss and the short thread on the tank means there can be no air lock because the underside of the immersion heater now protrudes well into the water. What a fiasco!

 

[batty]

Glad its sorted.

 

[reblle]

Hi very interested in this thread.I have changed several immersion heaters (+) with thermal cut outs over the last eighteen months or so.

The problems I have come across are usually once the cut out operates it can be reset but its not long before it trips again.I've tried renewing

the whole unit this lasts for a short time sometimes 1 or 2 weeks sometimes a month or so.The common thing is that most of the propertys use

only immersion heaters for hot water and storage heaters to heat the property i.e no gas etc. It seems to me that these type of immersion with thermal cut outs may have been brought in because of overheat problems with the traditional type of thermostat but they are not fit for purpose,

in my opinion they will trip out if the hot water remains at a high temperature (stored hot water not used).

I have contacted my plumbing organization they recommended not leaving the heater on 24/7 and fitting a timer and usually immersion heaters are a back up.I have also contacted one of the main suppliers of immersion heaters they said turn down the thermostat!I emailed them recently again and have not had a reply.My supplier could not help either.

In the end the last property I dealt with about a month ago I fitted a traditional thermostat and immersion so far this seems to working ok.Two of the other propertys went over to combi heating systems,previously warm air, one of the clients had been resetting the thermostat nearly every day another site had twin immersions mounted horizontally we replaced both but only the bottom one is used on the night time time tariff this seems to be working as well.

If immersion heaters are used as a back up this problem will not appear for some time as most people will use the boiler to heat the water and by then any warranty will have expired so a new heater will be fitted to replace one with hardly any wear.This must be a nice earner for manufacturers and retailers but a scam as far as I can see.

Sorry for the rant,any ideas?

thanks

---------- Post Auto-Merged at 21:42 ---------- Previous post was made at 21:31 ----------

Just been reading the previous posts again and noted change of cylinder.All the sites I referred to were 36 x 18 cylinders ,with the immersion mounted on the top as standard, apart from the one with the horizontal immersion.So should all these people have changed their cylinders.

 

[batty]

If its in the top that where it will be the hottest. I don't think i would be happy putting in as standard immersion or stat without a cutout would just not be worth taking the risk.

 

[Mikr]

Why thermostats trip

I was very interested to read this thread as I have experienced this problem myself this year. I have had problems with 3 different thermostats and decided to investigate. I took them out and had a close look at their operation in a separate tube of hot water and found that the problem appears to be with the switch contact itself. It is supposed to be a 'snap action' when the desired temperature is reached, but I found that in practice, the contact moved across very slowly. In circuit, this would create an arc when breaking the current and this arc heats up the surrounding metalwork in which the 'over temperature' trip is situated.

The reason for this incorrect action in my case was the assembly of the thermostat contact which was not aligned properly during manufacture. When I aligned the contact properly, the 'snap action' improved and the thermostat has operated normally for the last 2 or 3 months. This alignment is quite a precise and delicate operation and the contact spring must be completely clear of any obstruction and everything must be square. This does not seem to allow for any manufacturing tolerances.

This readjustment is not for the faint hearted and some recalibration might be necessary. It seems the design was optimized before the addition of the over temperature trip and I would say that in my opinion this is a design/manufacturing problem

It would be good to hear from anyone else investigating this in the same manner.

 

[SLIPSHOD & SLAPDASH]

Thanks for bringing up this old thread as i dont remember reading it before. There's a thread currently running with a similar problem so these need to be linked.

 

[Andrew Garwood]

I have found the problem. Its with the TeslaUK thermostat. Mine was tripping constantly. Its not the ambient temp of the cupboard or the water temp. The problem is the thermo casing itself is getting hot due to current thru the device. My brown and blue wires have heat damage and insulation gone hard. This is why it trips out before thermostat and water is only warm. After dissassembling the thermo (S230) it looks like the thermo contacts are pitted badly and evidence of burning. My guess is te contacts get worn and arcing causes excessive heat buildup.

Have replaced with a short S220 for now which works fine but I may contact TeslaUK as its only been 10 months installed.

You need to check the temp of the thermo casing after 5 mins and see if its really hot, also check the wiring for heat damage.

 

[Andy™]

id hope he's already fixed it, it has been over 5 years...

 

[Doc Hudson]

I think we can close this thread now. Probably best to start new topics on any similar issues.

Doc H.