Is it possible to add a hot water cylinder with immersion heater to a combi boiler

[51m0n]

We have a oil-fired combi boiler which has worked really well. However, we’ve just had solar panels installed and I want to use the excess power these are generating to heat water rather than export the excess power to the grid.

Is it possible to add a hot water cylinder with an immersion heater to a combi-boiler system?

Ideally things would work like this:
- immersion diverter would detect electricity export to the grid and divert this power to the emersion heater to heat the water instead
- when there is no export to the grid (eg when the sun is not strong) and the water temp in the cylinder falls the boiler would kick in and heat the water in the cylinder.

Thanks

 

[FiremanT]

We have a oil-fired combi boiler which has worked really well. However, we’ve just had solar panels installed and I want to use the excess power these are generating to heat water rather than export the excess power to the grid.

Is it possible to add a hot water cylinder with an immersion heater to a combi-boiler system?

Ideally things would work like this:
- immersion diverter would detect electricity export to the grid and divert this power to the emersion heater to heat the water instead
- when there is no export to the grid (eg when the sun is not strong) and the water temp in the cylinder falls the boiler would kick in and heat the water in the cylinder.

Thanks

You CAN use a combi to heat a cylinder, but you cannot have a cylinder serve the same taps as a combi.

You could use a cylinder to serve different taps to the combi, whether the cost and inconvenience would be worth it, even in todays market, is a consideration.

The cylinder would probably need a conventional power source for when th were e is not enough solar. Thus could be an immersion (don’t know if you could switch between domestic electric and solar or wether you would need a 2nd immersing heater), or you could run a coil off the combi

 

[Justin Passing]

You're going to store a cylinder of hot water than than use instantaneously? You're going to lose a few kWh a day from that. Only a couple if you insulate it like crazy, but...
You could store several kWh in the cylinder... do you need more flow ?
You could use a cylinder to preheat the water going into the combi - problems with that too.

 

[transam]

Solar ?

Used to be a set up marketed by Alpha which used a cylinder in conjunction with solar and there combi ??

Combi store if I recall ?? Is the name ????? I think ??

Afaik ?? Not all combis are able to accept pre heated water

Than there are flue heat recovery units ?? Vokera ? That pre heat the incoming mains water for combis

J&S afaik manufacture a combi ( or did) with an inbuilt flue recovery set up on there model think it is or was
J&S extra Reno model ??????

 

[51m0n]

Thanks for all the replies. Here are the answers to the questions and another idea.

Immersion diverter
There are things called emersion diverters that will detect when your panels are exporting power and send it instead to your emersion heater eg: https://www.deegesolar.co.uk/heating_your_water_with_solar_pv/ I think there is an override so that you can also power the same immersion heater from the grid if required.

Boiler types
If I changed my boiler, I think I'd go for an air source heat pump. However, I want to try and avoid doing this right now as the combi-boiler I have is fairly new (3.5 years old).

Storing hot water
Yes, I want to store the hot water rather than use in instantaneously. I accept there will be heat loss but this isn't too much of a worry as: 1) the power to create the hot water is virtually free (most of the time) and 2) a warm cupboard is a good airing cupboard.

An idea
What if I forgot about the hot water functionality of my combi-boiler (disabled it somehow) and treated the coil in the cylinder as another radiator? I'd need to figure out how to control this "radiator" differently to all the other normal radiators ie it would be on in the summer when the others are off and would need to be controlled according the temperature of the water in the cylinder not the temperature of the house.... (this could be a mad idea!).

 

[transam]

A combi is basically a systems boiler with added hot water producing bits

A combi does not have to be used as a combi can be used as a heat only systems boiler on s plan or y plan or what ever

Done it loads of times

 

[Justin Passing]

Your An Idea para 4 is how a non-combi heating system works.
Use a Y-plan rather than S-plan if your boiler needs volt-free contacts to turn it on. Your combi will have a bypass internally , = handy.
I'd keep the combi for the kitchen hot tap, because it keep your fresh hot water for cooking, drinks etc.
Run it by your boiler manufacturer or someone who knows the boiler in case there's something odd.

Your hot water won't be free on dull days, so stuff the cupboard with old duvets.

This should be in P & H.

 

[Bod ...]

A neighbour of mine has a 3 story house with combi on the basement floor and the bathroom on the top floor.


Mad system for the Size of house... I suggested using the combi hot water for the
Kitchen and utility and see if we could run a zone to top floor serving a cylinder.

I don't think he got it. Next thing he had some London crew fitting a new combi.

 

[bsr]

Hi @51m0n in simple terms yes this is possible and not unusual. Basically you stop using the hot water outlet on the combi and use the boiler as a system boiler. You then connect the heating output to the heating and tank via diverter valves and fit appropriate controls.

It's beyond DIY for most people though. One for a professional. I'm thinking £3k ish at the moment.

 

[51m0n]

Again, thanks for the very helpful replies. I agree this is beyond DIY but at least I have a better idea of what's possible when speaking to my P&H engineer.

 

[Justin Passing]

Not sure which bit is "beyond DIY"?

 

[gas112]

so how much free electricity do yo think you will be using to offset the cost of altering the existing system . . Pipework and fittings /couple of motorised valves / new programmer / new cylinder and tank or an unvented if you have the water pressure your prob talking a couple of grand

 

[JohnD]

If you have a modern gas boiler, the cost of HW is so low that you will not recoup the cost of a solar energy diverter.

 

[transam]

Went to an elderly couple yesterday

Hot water cylinder stat set at 65

Boiler stat at 55 (gas)

Hot water on 24/7

They use an electric shower

They Boil a kettle to wash up a few plates

Heating a cylinder 24/7 for what ??

Tried to explain it to them

but they were told it’s cheaper to keep the hot water on all the time

Oh well carry on than

 

[Odds]

Went to an elderly couple yesterday

Hot water cylinder stat set at 65

Boiler stat at 55 (gas)

Hot water on 24/7

They use an electric shower

They Boil a kettle to wash up a few plates

Heating a cylinder 24/7 for what ??

Tried to explain it to them

but they were told it’s cheaper to keep the hot water on all the time

Oh well carry on than

What would you recommend, in that case?