Greenstart 37CDi Combi CH Output

[D_Hailsham]

Does anyone know if it is possible to range-rate the CH Output of the WB Greenstar 37CDi Combi boiler?

I am in the middle of purchasing a house with this boiler and have estimated that the heat loss is no more than 15kW. The boiler produces 30kW max; I would like to reduce this, if possible, to prevent unnecessary cycling.

The boiler is nearly 11 years old, so there's a possibility that I may have to replace it fairly soon.

 

[Gasguru]

Yes there's a % setting for the heating output but normally doesn't need setting since the boiler is pretty good at ramping up/down and won't short cycle until the rads are up to temp.
11 years is nothing...all parts are available and there's no reason not to get 15 to 20 years life...unless there's been a distinct lack of servicing.
I have several early Greenstars with the same heat engines that date back to 2003.

 

[D_Hailsham]

It's good to know that the boiler should last several years more. However, it is vastly oversized for the heating loss, which I have calculated as 10.6kW. I have deliberately used worst-case figures to calculate this, e.g assuming an outdoor temperature of -5°C, 50mm insulation in the loft etc. The 37CDi has a minimum output of 9.4kW, so the boiler will be running in on/off mode if the outside temperature is above -2°C !!

Unortunately this is not unusual when combi boilers are involved as the heat output is geared towards HW requirment with CH requirements just an afterthought - particularly so now the requirement is reducing as insulation improves.

I have been researching boilers with low minimum outputs (below 3kW) and the lowest I can find is the Viessmann 200W B2HB which can go down to 1.7kW. This require a separate HW cylinder.The alternative is the Viessmann 222-F.

 

[OLLIE20]

As gasguru said wouldn’t be getting rid of that boiler regardless of your worries.

 

[Gasguru]

A wide turn down ratio ie. the Viessmann 200 (available as a combi too)sounds great on paper but I have Viessmanns own documentation from 10 years ago or so where they were actually highlighting how little the benefits were once you get past say 5 to1.
Just remember that these "extra eco" boilers tend to have pioneering design and are really a test bed for the future.
That Viessmann has a complete fan/gas valve/mass airflow sensor module...completely custom built for Viessmann using CAN bus comms. If it's not covered under warranty then it will be one huge cost that will wipe out several decades of potential savings (which are miniscule) from having a large turn down ratio.
Another one is the Vaillant Ecotec Green iQ with a turn down of 6 to 1. Again it's got additional complexities (flue gas analysis/mass air flow) to help achieve that but savings are easily wiped out if it's not covered by the warranty.

 

[D_Hailsham]

I have Viessmanns own documentation from 10 years ago or so where they were actually highlighting how little the benefits were once you get past say 5 to1.

Preumably Viessmann were saying that because they had not yet designed a system which could go beyond 5 to 1.

If it's not covered under warranty

Why wouldn't it be covered? It would be like a car manufacturer saying that the fuel injection syystem was not covered by the car's warranty.