Feasibility check - HIU and combi boiler replacement

[jumpman_23_]

Hello everyone,

I moved in into "new build" back in 2015. Single bed apartment with the following configuration in place:


1) Communal heating where HIU is installed in every flat.
Rossweiner heat sonic.

2) KINGSPAN RANGE TRIBUNE HE 210 LITRES UNVENTED VERTICAL PRE-PLUMBED INDIRECT HOT WATER CYLINDER

3) There's underfloor heating installed

4) No GAS


PROBLEM STATEMENT.

South East of London - extremely HARD water area. Over the years heating spiral inside the tank degraded. It barely able to heat the water up to 40C and it takes forever (very expensive nowadays).
Note aside: immersion still works but won't last long.


I would like to replace my current system. What i am looking for is:

1) I must keep HIU - that's untouchable.

2) I would like to get rid of the water tank it is occupying a lot of space in tiny apartment.

3) Instead i would like to have a combi boiler (electrical as there's no GAS). Instantaneous heater.

4) I would like to install water softener connected to the main before boiler. Currently it's not possible as there's no space for it due to water tank.



QUESTION

How will HIU work together with the combi boiler? Is it even possible?
What could be the right solution here?

I understand that replacing the tank likely to be the simplest one however it is not what i am looking for.


P.S.
I am even happy to switch off HIU flow, keep paying standing charge as long as I can get rid of the tank and install alternative heating solution that cost less and easy to maintain.

Irregular usage of the current system is what accelerate limescale production inside the appliances. Due to personal reasons it could be that I leave the system completely shut for weeks. Replacing a tank every <5 years is not a good option. Softeners, even the smallest still require some space that I can't allocate at the moment.


Any suggestion/recommendation welcomed!
Thank you so much

Art

 

[polesapart]

Over the years heating spiral inside the tank degraded. It barely able to heat the water up to 40C

Have you measured the flow and return temperatures to/from the cylinder coil?

 

[jumpman_23_]

You mean in my current system?
I have not.

 

[flameport]

Instead i would like to have a combi boiler (electrical

Doubtful if the electrical supply to a 1 bed apartment will be suitable for an electric combi.
Even if it was, performance will be mediocre and the cost will be high.

A 210 litre unvented seems excessively large for a 1 bed.
Much smaller cylinders are available.
If there really is no space for a water softener, this: https://www.combimate.co.uk/product/combimate-limescale-prevention-device is a much smaller alternative.

 

[Johntheo5]

While not addressing the water hardness issue one would think that the thermal charge would be based on a flow meter and the flow/return dT maybe measured on the HIU primary side so shouldn't have any effect on the running costs, to you.

 

[jumpman_23_]

@flameport - 210 litre unvented is what they put in every apartment irrespective of it's size.

Placing a smaller tank would get me some extra space (possibly enough to put a softener). However if there's a chance to get of the tank that'd be my preferred solution.


Could you please eloborate on that:

Doubtful if the electrical supply to a 1 bed apartment will be suitable for an electric combi. Even if it was, performance will be mediocre and the cost will be high.

You mean there won't me enough of power to run it? KWs?

thanks

 

[flameport]

An electric combi is typically in the 10kW-12kW range and would require a 100 amp supply to the property. It's exceptionally unlikely that a 1 bed apartment would have that.

Electrical supplies have limits, just as with anything else. It's not just a case of connect whatever you want and it magically works.

 

[jumpman_23_]

got it. Thanks.

But then if you think about it.. does it mean that typical user of combi boiler is someone who owns a private house and able to request/install more power from the supplier like E.ON (example).

 

[Johntheo5]

Also a 12kw combi will supply less than 6LPM at 40C for a shower which a lot of people wouldn't be happy with, most gas/oil fired combis are around 30kw to give greater than 14LPM.

 

[Harry Bloomfield]

got it. Thanks.

But then if you think about it.. does it mean that typical user of combi boiler is someone who owns a private house and able to request/install more power from the supplier like E.ON (example).

As above, a maximum domestic supply to a house is 100amps/ 10-12kw. Often the supply will be less than this. Larger than 100amps, then it would be normal to install (at a large cost) a 3ph supply.

 

[fixitflav]

As above, a maximum domestic supply to a house is 100amps/ 10-12kw. Often the supply will be less than this. Larger than 100amps, then it would be normal to install (at a large cost) a 3ph supply.

?? 100amp*230volt = 23kW

 

[jumpman_23_]

Thanks, it's clear. Electric combi boiler is a "no-go". Since I have no gas, i should forget about combi boiler.


Having a tank in my current setup seems to be a pre-requisite.
Therefore placing a smaller tank, saving some space inside the cupboard and installing a softener seems to be the only reasonable solution.

 

[jumpman_23_]

In case i decide to replace my current boiler/tank with something like this:

https://www.amazon.co.uk/Ariston-Electric-Inclusive-Manufactured-installed/dp/B093LQJX59/ref=sr_1_5?crid=1PCVEY5R0TGC&keywords=combi+boiler+100+liter&qid=1680976368&sprefix=combi+boiler+100+liter%2Caps%2C91&sr=8-5

Would i still be able to connect it to my HIU?

 

[flameport]

?? 100amp*230volt = 23kW

Theoretically yes.
In reality not going to happen, as the boiler won't be the only item installed in the property.
Power factor will reduce the maximum kW, 17kW is a more likely maximum with a 100A supply.
Anything above 12kW would also require a circuit breakers 63A and above, which most single phase consumer units do not have.
Such things would also be into the realms of causing significant volt drop on the supply which is likely to affect other consumers on the same transformer.

 

[flameport]

Would i still be able to connect it to my HIU?

No. That is an electric water heater, there is no provision to connect to anything else.

You need an unvented indirect cylinder, such as this: https://www.plumbnation.co.uk/site/worcester-green-storage-wb-90-litre-unvented-cylinder/ , plenty of others available in various sizes and shapes.
which would normally be heated from the HIU. It does have an electric immersion heater in it but that's only there as a backup for use when the HIU is broken.