Questions on 'keep warm facility' on combi boilers

[BriscsWK]

I understand the keep warm facility on combis should ensure a quick delivery of hot water, but could somebody confirm:

1, If a tap turned on, off and then on again in reasonably quick succession if only hot water will flow even if the combi had stopped firing; and

2, Can you run the hot water at a low level and still receive hot water - I believe on older combis a certain flow rate is needed for it to fire and heat the water?

Many thanks

 

[Agile]

I dont understand what you are asking on Q1.

All boilers ( except some storage boilers ) need a minimum flow rate to activate the boiler.

Thats usually about 2-3 litres per minute.

Tony

 

[BriscsWK]

Sorry if 'Q1' wasn't clear...

What I meant was:

Say you run the hot water tap to fill a washing up bowl and then turn it off. If you then turn the hot water tap on again (in a reasonable time frame i.e. before water cold in pipes) will you still get continuos hot water (as you do from my ancient vented system cylinder) coming through or will there be some cold coming through before the combi re-ignites?

Tks for your help and hope that makes it clearer...

 

[Agile]

You seem to asking a theoretical question!

The answer will depend on the type of combi boiler and the way it produces the hot water.

Tell me a boiler model and I can give you a specific answer!

I now wonder why you are asking!

Tony

 

[gas4you]

Years ago when gas was cheap and water expensive it could sometimes make sense to have the pre-heat on a combi set to on, to save water.

These days in 99% of cases it is totally unnecessary and only wastes expensive gas

 

[Agile]

Years ago water was not metered and so wasting water was not important.

I think the preheat facility is more about convenience and not wasting time than costs of use.

On a big heavy boiler like the Sine 18 using the preheat was very worthwhile.

Modern light construction combis give DHW within a few seconds so its pretty irrelevant.

The best was the PP Puma which always had a couple of litres of hot water in the heat exchanger ready for a hot tap to be opened.

Tony

 

[BriscsWK]

Reason for questions is that thinking of changing heating system and combi under consideration but people have told me tales of how long it takes for hot water delivery and that it is annoying - admittedly these people may have older combis - and I am not only interested in flow rates etc. but on convenience.

As for which make and type of boiler I think I am more confused now than when I started reading posts on this forum!!! I thought it would be either a WB or Vaillant but now I read of Alpha, Atag, Weissman, Buderus, Atmos, Mikrofill - not great when you are a decisive Libra

Are there efficiencies in having all new piping in addition to the obvious peace of mind re 40 year old burst pipes set in concrete?

Tks again for your help

 

[gas4you]

Personally I think there are only 2 choices. Best of the mass market is Vaillant, best end of, is ATAG

 

[spacethegas]

you've not considered Broag