Will an over sized boiler keep going on and off.

[coldboiler]

I have been looking at a Worcester Bosch 34cdi boiler for my 3 bed roomed house with 1 bathroom.

The gas engineer says it would be more appropriate to have a Worcester Bosch 30si as an over sized boiler will heat up to the required temperature and then turn off and keep repeating this on and off cycle. He says this is something to do with modulating, I don't understand how this works.

Can anyone advise whether or not an over sized boiler will cause problems?

My concern is that I get sufficient hot water to fill my king size bath. If I have the less powerful boiler will it just take longer to fill and if so will this be noticeable?

Any advise would be welcome.

 

[Ermintrude]

This a combi or do you have a tank? If it's a tank 100% for installer ( excluding fact he's a wb fairy)

 

[tom609]

The 30si can be range rated on central heating mode from 7.3 kw upwards and the 34cdi can be range rated from 7.7 kw the difference is at 35° rise the 30 gives about 10litres a min the 34 gives over 12ltres a min go on the worcster web site to get the accurate figures hope this helps

 

[dancinplumba]

Why Worcester tho' ?

 

[tom609]

Why Worcester tho' ?

Cos thats what the guy was asking about!! why confuse them

 

[IDCHAPPY]

Why Worcester tho' ?

I have a sneaking suspicion you don't like WB :lol:
I've fitted 2 in my whole career so i neither love nor hate them, just find them expensive

 

[TBServices]

It shouldn't present a problem, most combis will modulate down to 7-9ish kW. If range rated it stops the boiler firing too high to start with.

You should really base your combi sizing to suit your hot water requirements.

If you get a logic plus with a dedicated RF stat, the boiler knows how high to fire based upon the temp of your home = increased efficiency.

 

[Ermintrude]

Fit weather compensator on logic and it's even better

 

[TBServices]

Was told by tech not to use weather comp and opentherm together?