Small combi that does low temp so doesn’t cycle

Scot_39

Tanks have their limitations too.

A modern small tank loses (waste at least in summer) 1kWh - a larger one nearer 2  kWh - per day.

(That 1kWh over a third of my hot water heating in summer - as my shower and washing machine are cold fed).

And that doesn't included losses in the boiler and the heating loop to from the boiler  / and the hot water pipes from boiler - in some homes longer runs with a tank. 

If you dont already have a tank - finding the space for one in a small unit - can also be tricky. 

And if you think your heating demand is likely to be too low - the heat transfer - effective power - on the indirect coil inside the tank drops off very quickly as a function of temperature differential to tank bottom / mid temperatures ) and if set too low - may not effectively heat the tank  to target temperature.

This is only one persons tank and boiler set-up - but the fall off in temperature rise after about 10-15 mins and really slow rise towards the end - in his 1/2 hr 430pm to 5 pm boiler "burn" example demonstrates the problem with reducing effective power of the heating coil (its essentially delta T boiler vs tank water at contract surfaces) and boiler cutting in / out.  So average effective power goes sub the c3 kW mentioned above for those brands - which is average effective over the cycle.

https://forum.ovoenergy.com/home-and-heating-138/optimise-your-hot-water-set-up-17178

QrizB

doodling said:

The solution is either to accept (probably quite short) cycling when heating or go for the lowest power boiler you can get with a stored hot water system.

Hypothetically, and possibly not acceptable to the OP, you could borrow from heat pump practice and fit a volumiser tank to increase system volume and lengthen the cycle.

The cost (in money and floor space) might of course be disproportionate.

barker77

Just found these that might fit the bill 

https://www.cityplumbing.co.uk/p/vokera-vision-25c-combi-boiler-20097278/p/529743

https://www.cityplumbing.co.uk/p/vokera-vibe-max-combi-boiler-26c-20188719/p/634525

Apparently 3kw which seems best can do 

FreeBear

doodling said: The solution is either to accept (probably quite short) cycling when heating or go for the lowest power boiler you can get with a stored hot water system.

Even with a heat only boiler, I think you'll struggle to find anything that will modulate below ~3kW. And if you do, expect to pay £1200 (plus fitting) or more.

MWT

FreeBear said:

doodling said: The solution is either to accept (probably quite short) cycling when heating or go for the lowest power boiler you can get with a stored hot water system.

Even with a heat only boiler, I think you'll struggle to find anything that will modulate below ~3kW. And if you do, expect to pay £1200 (plus fitting) or more.

We have a 19kW Vitodens (heat only) and that still doesn't go below 3.2kW.