What can go wrong with an immersion water heating system?

[LeanTwo]

My old Economy7 water cylinder started leaking so I had a new one installed.  Both the old and new cylinders have an indirect coil from our multifuel stove as an auxilliary top-up.

 

The water temperature from my new cylinder, in a morning is just lukewarm.  Sadly the old tank started leaking but it did deliver a tank full of lovely hot water each day.  I have checked the obvious things like the electrical switch for the supply to the immersion is in the on position, the thermostat is set to a hot setting (70°C) and whether the RCD had been tripped.

 

What else could have failed in my system?  Any advice or suggestions would be great.

[JohnMo]

We have a thermal store, with immersion.  When heated by electricity only, it would only get to about 48 degrees, even with the thermostat set at 70.  Replaced the thermostat the same outcome.  In the end I wired in an external thermostat and all was fine.

[Conor]

Have you checked the thermostat on the actual immersion coil unit? You'll need to isolate it and take off the palstoc cover to access it.

[LeanTwo]

32 minutes ago, Conor said:

Have you checked the thermostat on the actual immersion coil unit? You'll need to isolate it and take off the palstoc cover to access it.

 

Hi Conor and thanks for your reply.  Can you describe what you mean by the "palstoc" cover.  Is this the cover  on the end of the thermostat with the temperature dial on it? 

[LeanTwo]

45 minutes ago, JohnMo said:

We have a thermal store, with immersion.  When heated by electricity only, it would only get to about 48 degrees, even with the thermostat set at 70.  Replaced the thermostat the same outcome.  In the end I wired in an external thermostat and all was fine.

Thanks for the reply John.  Pity that we have to go to these lengths when the theremostat should work! Thanks for the tip.

[ProDave]

The immersion heater is a round thing near the bottom of the tank with a thick cable entering it.  It will have a round cover sometimes plastic, sometimes metal, usually secured by a single bolt.  You need to remove that cover to see the thermostat for the immersion heater.  Post a picture of it here.

 

Any other thermostat with a visible dial and usually higher up the tank is nothing to do with the immersion heater.

 

Why not just call the installer that fitted it back and tell him it is not working since he fitted the new cylinder.

[LeanTwo]

Thanks for the reply Dave.  Sorry, I should have told you that I took the cover off to read the thermostat setting.  I have called the installer but he hasn't returned my call yet.  I will try again.  I wanted to check that I hadn't missed something.

Edited November 29, 2022 by LeanTwo
Spelling correction.

[LeanTwo]

Thanks for all the replies.  The plumber came back to check the installation. As part of this he revisted the consumer unit to find that he had left the Economy7 main isolation switch in the off position.  Soon rectified.

[Caddy]

@LeanTwoCan I ask what make and model your new tank was please? My stove and tank are to be renewed at sometime in the next 12 months and I was think of maybe getting a stove with a boiler to help with HW heating. I'd be interested to know your set-up. Cheers.

[Iceverge]

On 06/01/2023 at 16:23, Caddy said:

@LeanTwoCan I ask what make and model your new tank was please? My stove and tank are to be renewed at sometime in the next 12 months and I was think of maybe getting a stove with a boiler to help with HW heating. I'd be interested to know your set-up. Cheers.

 

Have you an unvented DHW system or an open vented one? 

[Caddy]

On 08/01/2023 at 17:09, Iceverge said:

 

Have you an unvented DHW system or an open vented one? 

Vented currently. I know you cannot connect a solid fuel boiler to a un-vented tank (unless you want to make a bomb....). My hot water is electric currently like the OP. I've been looking at a secondary heat source for it, either solar thermal or a new stove maybe. Not enough just from the Eddi in winter.

 

[Iceverge]

I've just installed a vented thermal store for my parents. It's working well so far. Balanced pressurised hot and cold is vastly superior to gravity fed. 

 

For your situation it might be simpler and cheaper to install an exhaust source heat pump like @Thedreamer if you have much pipework to revisit. 

 

Use the immersion via solar in the summer and the heat pump to harvest excess heat from the stove in the winter at a COP in excess of 3. 

 

 

[Caddy]

On 09/01/2023 at 18:44, Iceverge said:

I've just installed a vented thermal store for my parents. It's working well so far. Balanced pressurised hot and cold is vastly superior to gravity fed. 

 

For your situation it might be simpler and cheaper to install an exhaust source heat pump like @Thedreamer if you have much pipework to revisit. 

 

Use the immersion via solar in the summer and the heat pump to harvest excess heat from the stove in the winter at a COP in excess of 3. 

 

 

@Iceverge I been looking at exhaust air heat pumps and don't they really need to be used in conjunction with a MVHR system to duct the recovered air to the intake? I'm trying to decide whether to bite the bullet and go full heat pump with UFH and take the fiscal hit or go A2A for room heating and sort out another method of supporting the PV for HW in the winter like a stove with back boiler.

[Iceverge]

You can get exhaust air heat pumps for DHW only. In fact the exhaust air heat pumps for space heating are a bit like trying to invent perpetual motion. The energy needs to come from somewhere!

 

 

Here's an example of a DHW ESHP. You get excellent COP with the elevated temps that the heat pump can harvest. A2A or stove heating the air means you'll get air to water heat pump running costs without all the plumbing trouble and cost.