How Long For Hot Water?

[aintsohandyandy]

Is it normal for the water to take about 30 secs or more to run hot from my kitchen sink? This seems like a very long time especially when on a water meter!

The system is run from a Baxi 105e combi-boiler. The house is a 3bed detached house (approx 1000 ft2).

 

[Bahco]

It would depend on how far the boiler is away from your sink.
My boiler is upstairs and I have the same wait

 

[nstreet]

It will also depend on how well your hw pipe is insulated and whether or not in runs in any solid wall or floors. If nothing else, put some climaflex insulation on the hw pipe wherever possible.

Our pipes run in the ceiling void and in the concrete floor and no, the floor encased ones aren't insulated. So each time you ran a little hot and then turned off and ran a little more it comes out cold. Since insulating all of the pipework in the cleiling void its not quite as bad.

 

[ChrisR]

Oooops. I'll leave this here but it would not be usable with a combi - which I only just noticed the "customer" has.

I have an "unvented" 10litre undersink heater (stored, electrically heated) for one installation, where the wait was even longer. This means the first water from the tap is piping hot, but if you want more than a basin full of (mixed) hot water you have a long wait (eg 30 sec) until the hw from the cylinder finally arrives.
It's a bit odd and its a compromise, but the customer is happy.
Technically its easy because the heater is only 2 kW, and there's no need for lots of protection on the hw pipes because the supply is vented. Best to check with the mfr for their current view on that though.

 

[ln1234]

Could a secondary return be used in this instance to keep the water in the pipes hot (at certain times)? I'm not sure if doing this with a combi would be much different than with an unvented cylinder.

 

[ChrisR]

There's nowhere to connect your secondary return TO on almost all combis, so no you couldn't. I suppose you might be able to do something with a pump and valve, but I've never heard of anyone doing it!

Check the pipe diameters - its possible someone has reused some old 22mm, which would increase the delay.

For 15mm pipe you have about 7 metres per litre. (3m for 22mm) Your flow should be 10 - 12 litres per minute, say 6 l in 30 secs.
So is there possibly 42 metres of pipe between the tap and the combi?
Presumably not, so measure how long it takes for the HW pipe out of the combi to get warm when you turn the tap on. NB they do make a version of this combi with a store of water to draw off imediately, called the "instant"!!

 

[Agile]

The other aspect no one has mentioned is how quickly the boiler fires up.

That varies between models, the ideal response takes 12 seconds because it needs to purge the combustion chamber. Most other modern boilers will fire up in 2-5 seconds.

If there is a litre of water in 7 metres of pipe then its six seconds to get a litre out of the tap and few new installations have much more that this distance in compact properties. Bodges through the loft excepted!

Tony Glazier

 

[ChrisR]

Firing up time is covered by

measure how long it takes for the HW pipe out of the combi to get warm when you turn the tap on

 

[dg123]

Does this type of boiler has a reservoir? The boiler I have (condensing combi) will either keep some water heated or will heat only on demand. I have it set to only on demand as it uses less gas but when hot water is required it takes longer to get.