Faulty Immersion element stat?

[Gary K]

I have just had a new boiler and 210 ltr unvented tank fitted in the loft to replace a very old Baxi back boiler. I have now fitted a Solic 200 diverter to utilise all the spare capacity from the 3,84 Kw Pv system on the roof. This has only just become an option as the old existing tank did not have an element fitted and I was told that the chances of fitting one to the old tank without damaging it were slim to none!

The issue that I have, after checking the element that is fitted to just below the middle of the tank is that the thermostat appears to cut out a lot earlier than I expected. According to the manufacterers website, the element should when turned to maximum, should cut out at 70deg/C, having a red tag, although on the cover of my element, it states 65deg/C
As the sun is out today, I have had a bath rather than the normal shower and the water has been heating via the diverter for 90 mins or so and has taken 3.23Kwh of power but has now cut off due to the thermostat on the element.

Having done some very rudementary checking with a meat probe (which does measure 100deg +/- when put in a boiling kettle), the hottest point on the hot water take off pipe and also under the nearest hot tap after running off some water is 50deg/C, which believe this is only just hot enough to kill off Legionaires desease. I can heat the water to a higher temperature if I use the new boiler but i think the element should be able to get to 65deg by its self before cutting off
Obviously, I have checked that the immersion stat is set as high as possible so would it be fair to assume that the thermostat is not acting correctly and is cutting out prematurely. Would I have reasonable grounds to contact the fitters/ manufacterers and request a replacement element?

 

[Murdoch]

What happens if you push the boost button on the solic ?

 

[Gary K]

What happens if you push the boost button on the solic ?

Once the thermostat on the element has cut out, Nothing. Obviously, it cannot bypass the thermostat

 

[fowlerboi]

Most low temp systems use an immersion to do a weekly Legionnaires heat up to over 60, it's not something that needs to be done constantly. But thats not the point for your issue.

Is it just single immersion? That immersion is really high for a PV system which intends to mostly use the immersion, a double immersion cylinder would have been better.

With the immersion maxed out it should hit 60 which is what the instructions say. The 75*c cut out is a secondary protection with a non-self reseting switch.

Can you leave your immersion on overnight using the grid, that way you remove the variable of your controller. If it's not 60 in the morning before water is drawn off then I would expect the engineer back to change it.

 

[Gary K]

Most low temp systems use an immersion to do a weekly Legionnaires heat up to over 60, it's not something that needs to be done constantly. But thats not the point for your issue.

Is it just single immersion? That immersion is really high for a PV system which intends to mostly use the immersion, a double immersion cylinder would have been better.

With the immersion maxed out it should hit 60 which is what the instructions say. The 75*c cut out is a secondary protection with a non-self reseting switch.

Can you leave your immersion on overnight using the grid you remove the variable of your controller? If it's not 60 in the morning before water is drawn off then I would expect the engineer back to change it.

Hindsight is wonderful!
I assumed that the immersion would be at the bottom as this makes sense and only noticed it wasn't when the fitters unpacked it on the morning of install, bit late by then!
Single immersion only just below half way but thats still about 100ltrs above and it will heat below to a certain amount.
I cant really leave on overnight as it is only powered via the Solic and the boost only works for 90mins but I can check visually when the device has power available for the element and it has for most of today as we generated nearly 11KWh and the diverter only sent 3.95KWh. I have it on a monitorable 3 pin plug so I can see what power is going through it at any time so its not hard to see when the stat has cut off.

 

[fowlerboi]

I'm not familiar with the controller you're using but as long as you can confirm its the stat clicking off and not the controller then it points towards replacing the immersion. But confirm this with a test over a decent period of time with no usage

100L for an unvented isn't a lot as showers can use over 10lpm (all be it not all hot water) and your recovery time will be fairly long. See how you get on with it but either a different cylinder or a destrat pump might be in order if you intend to heavily rely on the immersion

myenergi-De-stratification Pump install

Hi All, given the amount of De-stratification I'm suffering in my tank (up to 40 degrees between top and bottom) I'm thinking of installing a de-stra

myenergi.info

 

[Gary K]

I'm not familiar with the controller you're using but as long as you can confirm its the stat clicking off and not the controller then it points towards replacing the immersion.

100L for an unvented isn't a lot as showers can use over 10lpm (all be it not all hot water.) See how you get on with it but either a different cylinder or a destrat pump might be in order if you intend to heavily rely on the immersion

 

[Gary K]

Something odd in the above post that I replied to- the link for the destrat pump was considered spam and I was unable to post a reply without deleting it - although it was accepted at time of posting.
There is an instantaneous shower fitted. Not sure if its feasable to get a thermostatic unit fitted to the bath taps as it would need a long hose fitted to reach the other end of the shaped bath.
Replacing the aged Baxi system was top priority as it was only 65% efficient when new- could be 40 yrs old, fitted before I bought the house so the new Baxi at over 97% should save a few quid and anything heated by the solar is a bonus. Today you can see the element turn back on whenever the hot water tap is turned on to wash up etc and then turn off after 15mins or so and although the sun has been out, generation is considerably down compared to the summer months when 24KWh is not uncommon so I expect to turn the heating off completely.

I have already looked into a destrat pump but obviously need to get the new system working correctly first before making a decision as the pumps aren't cheap.
The installers have got to come back as they are committed to reconnecting the front fire that is part of the back boiler system - they guy who priced up the job did not notice that the gas pipe that feed the fire was not sleeved and although this was acceptable 40 years ago, it is now considered immediately dangerous so they capped off the gas pipe. I have since cleared the brickwork from around the pipe so they can take off a bend to fit a sleeve reconnect and certificate. When they get in contact , I will suggest that they bring their own thermometer so we can check accurately what temp it is cutting out at.

Looking at the thermowatt site, some "blue" elements should be adjustable to 71deg and the emergency cutout is a very high 85! I didn't realise that the stat can be swapped from the element so its quite a simple job for the installers!

 

[fowlerboi]

https://www.tanks-direct.co.uk/files/pdf/pdf30310.pdf

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