Boiler Power (KW) setting?

[berty3000]

Hello,

I have a Worcester Greenstar 25i. Settings include the following:

2.1A (Max CH power [LowNox below 13KW] )

Current setting: 24KW.

2.1B (Max DHW power)

Current setting: 25KW.

Do the settings need to be this high for a 3 bed house with 9 radiators? If not, what recommended instead? Is this something I can just change without other adjustments?

Thanks

 

[ianmcd]

yes you can change them if you want cold showers, settings seem about right, you are lucky not too many installers would have set that up properly

 

[berty3000]

yes you can change them if you want cold showers, settings seem about right, you are lucky not too many installers would have set that up properly

The CH setting is on maximum 24KW though. Is this necessary for heating a home and heating system the size of mine? What I've read online is that more like 10KW would be sufficient, but I'm not sure if it is wise to just change this setting if there could be undesirable repercussions.

I have the water temperature set to 45C and that is fine. If 25KW is necessary to heat the water then I'm happy leaving as is.

 

[ianmcd]

The CH setting is on maximum 24KW though. Is this necessary for heating a home and heating system the size of mine? What I've read online is that more like 10KW would be sufficient, but I'm not sure if it is wise to just change this setting if there could be undesirable repercussions.

I have the water temperature set to 45C and that is fine. If 25KW is necessary to heat the water then I'm happy leaving as is.

Sorry misread your post I thought you said CH maxpower was 13 KW which would be about right for your system or possibly lower, but yes you need the DHW set to max 25KW

 

[Madrab]

I have the water temperature set to 45C and that is fine

Be careful about that. Any HW storage should be raised to over 50Deg at least once a week and run through any low use HW legs/circuits. This is to ensure that any legionella bacteria that may be present a killed and flushed through.

This is becoming more of an issue and more relevant with the uptake of low temp systems and AS/GSHP's

 

[berty3000]

Be careful about that. Any HW storage should be raised to over 50Deg at least once a week and run through any low use HW legs/circuits. This is to ensure that any legionella bacteria that may be present a killed and flushed through.

This is becoming more of an issue and more relevant with the uptake of low temp systems and AS/GSHP's

It's ok, I don't have a water tank. Just a combi boiler. There are a few dead legs in the system, not sure how much of a risk they are (where older pipe runs capped off for whatever reason). Would you be concerned by this?

 

[berty3000]

Sorry misread your post I thought you said CH maxpower was 13 KW which would be about right for your system or possibly lower, but yes you need the DHW set to max 25KW

So can I just lower the max CH power to 12KW without making any other changes? Is there any risk of damage?

I've already reduced the pump head setting to the lowest, which has been fine and am trying to make other efficiencies, and ensure boiler is working in the best way.

 

[berty3000]

According to this, a house my size and type could even work with 8KW... although I think the minimum for my boiler is over 8KW, so could maybe try 10KW for the CH?

Use our boiler size calculator tables

Don't oversize your boiler, it will be less efficient. We guide you on correct boiler sizing principles.

www.theheatinghub.co.uk

 

[Madrab]

It's ok, I don't have a water tank. Just a combi boiler.

There are a few dead legs in the system, not sure how much of a risk they are (where older pipe runs capped off for whatever reason). Would you be concerned by this?

As part of a landlords safety inspections, I complete a Legionella risk assessment where required. That includes inspecting all accessible hot and cold pipework and looks for areas that could present a risk. One of them is dead legs.

It is then incumbent of the landlord to reduce that risk as low as possible, that includes the removal of dead legs.

If they can be removed then I would recommend that they are.

As far as range rating your boiler to match your system then you really need to measure up your rads (hopefully they were sized properly for the room they are heating), check their output at your given system temp, add that up and add at least 10% (actual system pipework size dependent) for the heat loss through the pipework etc. That then would be starting point you would range rate your boiler to.

 

[berty3000]

To be honest, I don't think the dead legs relate to the water supply. More to do with gas or central heating.

I will have to look into this rating and maybe get a plumber to assess it when I get the boiler serviced. For now though, on the basis of a 3 bed house that is well insulated, with 9 radiators (several of them small), generally insulated pipe in the attic, would it do any harm to try 10KW rather than the current 24KW? What is the worst that will happen, just won't heat up well if not enough?

 

[Harry Bloomfield]

I will have to look into this rating and maybe get a plumber to assess it when I get the boiler serviced. For now though, on the basis of a 3 bed house that is well insulated, with 9 radiators (several of them small), generally insulated pipe in the attic, would it do any harm to try 10KW rather than the current 24KW? What is the worst that will happen, just won't heat up well if not enough?

You can play about with that setting, to your hearts content. The worst that can happen, is that you will not be warm enough, when it is really cold.

 

[berty3000]

You can play about with that setting, to your hearts content. The worst that can happen, is that you will not be warm enough, when it is really cold.

What is the benefit to lowering it, less gas used?

I have lowered it to 10KW and all seems well. It took a little longer for the radiators to heat up. The boiler seems to be running more constantly, rather than stopping for breaks.

I now have it on the lowest pump head setting.
10KW max output.
Flow temperature is 52C.

How do we know what the significance of the pump head setting is versus 1KW output higher or lower?

Also, there is still only 5C difference in the flow and return temperature as far as I can tell. The boiler says 52C on the gauage, I measured about 46C on the pipe as it leaves the boiler, and return pipe is about 41C.

 

[JohnD]

What is the benefit to lowering it, less gas used?

No. If it takes 20kWh to heat your house for a day, the boiler will just run longer, and be slower to heat up from cold.

If you reduce power enough, the house will just be cold. That will use less gas. You could also achieve a cold house by turning the thermostat down. Do you want a cold house?

 

[Harry Bloomfield]

What is the benefit to lowering it, less gas used?

The boiler will modulate down, work more efficiently, and burn less gas.

I have lowered it to 10KW and all seems well. It took a little longer for the radiators to heat up. The boiler seems to be running more constantly, rather than stopping for breaks.

Exactly, stop/start wastes gas, a steady low burn is more efficient. Just increase the 10Kw, if it takes too long, or fails to provide enough heating when it's really cold.

 

[Harry Bloomfield]

How do we know what the significance of the pump head setting is versus 1KW output higher or lower?

Run the pump as low as possible, consistent with the radiators having enough flow to heat them up.