Combi boiler modulation for low heat output

[LoneWolf]

I'm looking to buy a 24kW combi boiler with only 4 radiators rated at 1.7kW each, so I can later expand and add more radiators.

I expect relatively low heat dissipation from the heating circuit.

If I run the boiler from cold, the water heats up to say 40 degrees in the heating circuit and the boiler shuts off. At what point would it turn on and why is modulation important? Couldn't the boiler turn on when the heat in the radiators drops substantially to avoid cycling on and off and work just fine with low modulation?

I will only have 6.8kW from 4 radiators at max power. When they heat up, I expect that would drop considerably, even with 1:10 modulation I would probably have too much power so the boiler would need to switch on and off repeatedly regardless?

 

[Aire]

This is maybe more a conversation you should have with a manufacturer, also look at different combis because the kw rating is the hot water rating, generally the heating output differs. A baxi 624 has 25kw on hot water but 20kw on heating, non condensing output has a minimum of 6.8kw so your boiler won't really go in condensing mode but should modulate just enough to not cycle. Although I'm not an expert on boiler modulation so I could be wrong.

 

[Scott_D]

You can set the heating load and anti cycle time on vaillant

 

[Drewy]

Viessmann Vitodens 200-w. 1:20 modulation down to 1.6kw and you can range rate it. Perfect!!