Low KW boiler needed

[graeme m]

We need a low out put boiler 10kw (or less) would be ideal. There's only three rads (ensuite, Bathroom, hall) water tank heated by solar and boiler as back up.

Any suggestions?

[Guest Alphonsox]

Gas, Oil, LPG, Electric, wood or other ?

[CC45]

Gas? Oil? Thats going to be tricky.  A bigger one that can modulate down may be a solution. 

[Temp]

I think the problem is finding a small combi. Less of a problem if you want a small system boiler feeding a hot water tank.

 

WB have 9 and 12kW gas system boilers.

 

https://www.worcester-bosch.co.uk/products/boilers/directory/greenstar-i-system-9kw-to-24kw

 

Pretty sure they modulate down to 30% but best check with them. If that's correct then I think your rads still need to total over 3kW. 

 

 

Edited June 18, 2018 by Temp

[Alexphd1]

I remember a worcester greenstar combi that had the option of changing a chip so the heating output was 12kw?? 

Edited June 18, 2018 by Alexphd1

[Temp]

As I understand it you need a large burner in a combi to provide the flow rate needed for a shower. This determines the minimum burner size which is also used to provide the central heating.  It's not (such) a problem for a system boiler because they don't have to instantly heat the water for a shower. Instead it's the hot water tank that provides the high flow rate needed.

[Nickfromwales]

Iirc the WB Greenstar 12ri will drop to 6-7kW. That's what you want. 

[Alexphd1]

16 minutes ago, Temp said:

As I understand it you need a large burner in a combi to provide the flow rate needed for a shower. This determines the minimum burner size which is also used to provide the central heating.  It's not (such) a problem for a system boiler because they don't have to instantly heat the water for a shower. Instead it's the hot water tank that provides the high flow rate needed.

  

That would make sense but not really. Pre ERP (haven't worked on latest genetarion) worcester greenstar boiler had two burners. One burner was shared from 12kw system to 30kw combi. Apart from the DHW side being added the only thing changed was the chip on the pcb which changed the speed of the fan.

 

Always confused me when the charged so much for the 40kw heat only boiler!! 

[graeme m]

sorry gas.

 

[graeme m]

20 hours ago, Nickfromwales said:

Iirc the WB Greenstar 12ri will drop to 6-7kW. That's what you want. 

Yeah that's looking the likeliest option. What's the reliability of WB these days, my Mother's one was terrible, 7 years old and broke down every year.

 

[Nickfromwales]

Much as it pains me to say it, they're a good machine these days. 

Go for it. ?

[Temp]

On ‎18‎/‎06‎/‎2018 at 16:52, Alexphd1 said:

worcester greenstar boiler had two burners

 

Interesting.

[Alexphd1]

23 minutes ago, Temp said:

 

Interesting.

Just reading my comment back it is not 100% clear. WB had two main burners in the whole range. The round one(ri, I and si) made in the UK 12-30kw and the square one (cdi) made in Germany 25-42kw. 

Sorry to get off topic again. 

[Nickfromwales]

23 hours ago, Alexphd1 said:

Just reading my comment back it is not 100% clear. WB had two main burners in the whole range. The round one(ri, I and si) made in the UK 12-30kw and the square one (cdi) made in Germany 25-42kw. 

Sorry to get off topic again. 

Never apologise for adding information to a thread  

 

To make this crystal clear, the 2 burners comment is not a reference to any one boiler having two burners inside it. 

The lower kW range of boilers utilises one type of burner at the point of manufacture, and the higher kW range utilises the other.  

The lower range burner will drop down to 6-7kW at maximum modulation iirc, and the higher range burner does around 9kW.

Maximum Modulation = lowest heat that the gas valve / burner can output when full output is not required / necessary. 

Edited June 21, 2018 by Nickfromwales