Background .... for a new SelfBuild I installed NuHeat underfloor heating on both floors.

Been in and working well for 18years

 

However the Baxi Barcelona boiler is proving very unreliable, now at the point when it fails it's hard work getting maintenance company to agree to fix it ..(beyond economical repair)

The boiler is HEAT only, pressure vessel, pump, thermostat are all external and part of Nu-Heat system, and is set to 30kW output power.

 

Originally NuHeat were very helpful and as part of the design, recommended the boiler.   However now they are not willing to help and advise boiler should be specified by my 'heating engineer'   ..... when they know that the heating system design was done by them, they were only engineers involved.      GasSafe engineer used for gas connection and commission only ...... NuHeat is sold as DIY install for SelfBuilders.

 

So I need to find a 28-30kW  condensing HEAT only boiler.    I want to have a stainless steel heat exchanger, and it needs to connect to a thermal store.

The last 2 requirements are proving difficult ..... Valiant do nice boilers but will not allow connection to a thermal store.

BAXI do the 600 & 800 HEAT  but while they have stainless steel heat exchangers on System boilers ... only aluminium on HEAT range.

 

So far my only option is the Intergas OV range ..... 

 

What boilers are you using on UFH ?

So are you just heating the thermal store, the UFH flow coming off the thermal store?  Or are you heating the thermal store and the UFH flow is separate?

I just need a HEAT only boiler to connect the primaries to thermal store - no other connection to boiler side.

Edited August 16, 20224 yr by sargan

You just need a boiler that can connected to a vented system. As most of the housing stock in the uk is fitted with a vented system (header tank in loft) it shouldn't be that hard to find one.  I assume your thermal store is open vented - either loose lid on top of cylinder or header tank

 

Here are 99 of them - you are looking for a heat only boiler not a system boiler, system boiler need to connect to a pressurised system.  The boiler doesn't know if its connected to an open vented DHW cylinder or radiator or a thermal store.

 

https://www.screwfix.com/c/heating-plumbing/boilers/cat6660001#category=cat6660001&boilertype=heat_only

forgot to mention, if you are heating TS via a coil any a system boiler would be needed.  If direct heating a heat only boiler.

 

On 16/08/2022 at 10:14, JohnMo said:

So are you just heating the thermal store, the UFH flow coming off the thermal store?  Or are you heating the thermal store and the UFH flow is separate?

The Thermal store is connected to boiler .... everything else come off Thermal store.  Pic may help

On 16/08/2022 at 13:17, JohnMo said:

You just need a boiler that can connected to a vented system. As most of the housing stock in the uk is fitted with a vented system (header tank in loft) it shouldn't be that hard to find one.  I assume your thermal store is open vented - either loose lid on top of cylinder or header tank

 

Here are 99 of them - you are looking for a heat only boiler not a system boiler, system boiler need to connect to a pressurised system.  The boiler doesn't know if its connected to an open vented DHW cylinder or radiator or a thermal store.

 

https://www.screwfix.com/c/heating-plumbing/boilers/cat6660001#category=cat6660001&boilertype=heat_only

  No Thermal store (and hence primaries )is pressurised (1 bar).    

Agree as per OP .... its a HEAT only boiler I want.

Edited August 22, 20224 yr by sargan

On 16/08/2022 at 13:22, JohnMo said:

forgot to mention, if you are heating TS via a coil any a system boiler would be needed.  If direct heating a heat only boiler.

 

Thermal store contents is circulated around boiler.

The DHW circuit and UFH both have own transfer coils/heat exchanger

My investigations have shown 3 options (options worth considering)

 

Veissmann Vitodens 100-W  in 30kW  .. has advantage of excellent build quality and a full stainless steel  INOX heat exchanger.

 

Intergas HRE 30 OV  in 30kW  ... while not stainless heat exchanger it is copper, disadvantage, no GasSafe guy I have contacted has heard of them, no approved installers anywhere near me (75 miles)

 

Worcester Greenstar 8000 Life 30kW   .. expensive for a standard aluminium heat exchanger boiler, a lot of money for what it is.   Positive is they give a full 10 year guarantee ... anything at all part & labour covered. Much better than warranty,

 

 

My GasSafe guy used to be Veissmann approved installer, which would get me 10yr warranty .... if he can get 're-approved' then Veissman may be the choice.   If not then the Worcester.

I’d go for intergas…. Either a heat only or a combi (just set it up to heat only in the settings). As they use a dual path heat exchanger and don’t contain a diverter, you can use nearly any of their combis as a heat only.

I have an Atag boiler, very few parts inside and really quite.  As said any combi can be configured to run the way you want it.  You can even add an on demand hot water circuit from the combi, so an outlet like the kitchen never runs out of hot water.

Would not use a combi on a Thermal tore - don't think that is an efficient way to use them.

 

Anway decision now made ...

 

Heart said Intergas, but could find nobody in area who would install, most had never heard of them.

So went for option 2  .... Viessmann Vitodens 100-W Heat only.

Great reputation, and a key point for me a stainless steel heat exchanger.

Comes with 10yr warranty as standard, and got price down to £1,024  (Incl flue) so good deal.

I have a similar age nuheat system. I'm using a system boiler which has an internal pump (and thermo stat). It works ok with an extra relay external to the nu-heat controller board arranged so that the boiler gets a call for heat and runs the pump when the flow switch is triggered (also over-riding the cylinder stat and relying on the boiler stat). It works, but is far from ideal so my long term plan is to drop the energy master thermal store, replace with an unvented cylinder and switch to a heat pump directly running the UHF at low flow temp.