I have one, and I find it quite difficult to get the flow right to
give optimum amount of hot water.

Would it be worth putting an in-line valve on the cold inlet to the
boiler and then adjusting it such that I could set it to the flow
which would be optimum temperature when taps turned on full? ie it
would limit the flow to a max value which would produce hottest water.

If yes - could I adjust by trial and error or could I adjust and set
to a known litres/minute to get the optimum flow. How could I find
out what that optimum flow would be - I guess it would be part of the
spec of the boiler?

"Pete" wrote in message
news
I have one, and I find it quite difficult to get the flow right to
give optimum amount of hot water.

Would it be worth putting an in-line valve on the cold inlet to the
boiler and then adjusting it such that I could set it to the flow
which would be optimum temperature when taps turned on full? ie it
would limit the flow to a max value which would produce hottest water.

If yes - could I adjust by trial and error or could I adjust and set
to a known litres/minute to get the optimum flow. How could I find
out what that optimum flow would be - I guess it would be part of the
spec of the boiler?


Won't work. The groundwater changes temperature over the year by 10C.
Why don't you just adjust the DHW temperature dial on the combi on an
occasional basis - I adjust it every so often during the year on my Vaillant
to keep the water around the 50C mark.

Andy.

On Sun, 12 Nov 2006 19:12:10 -0000, "Andy"
wrote:


"Pete" wrote in message
news
I have one, and I find it quite difficult to get the flow right to
give optimum amount of hot water.

Would it be worth putting an in-line valve on the cold inlet to the
boiler and then adjusting it such that I could set it to the flow
which would be optimum temperature when taps turned on full? ie it
would limit the flow to a max value which would produce hottest water.

If yes - could I adjust by trial and error or could I adjust and set
to a known litres/minute to get the optimum flow. How could I find
out what that optimum flow would be - I guess it would be part of the
spec of the boiler?


Won't work. The groundwater changes temperature over the year by 10C.
Why don't you just adjust the DHW temperature dial on the combi on an
occasional basis - I adjust it every so often during the year on my Vaillant
to keep the water around the 50C mark.

Andy.


But if it was done in the winter then this would be worse case
scenario wouldn't it?

Pete wrote:

I have one, and I find it quite difficult to get the flow right to
give optimum amount of hot water.

Would it be worth putting an in-line valve on the cold inlet to the
boiler and then adjusting it such that I could set it to the flow
which would be optimum temperature when taps turned on full? ie it
would limit the flow to a max value which would produce hottest water.

Yes this can work (although obviously you need to adjust the flow
restriction as the groud water warms up in the summer). You may find the
boiler already has a service valve on the cold inlet that you can
partially turn off.

If yes - could I adjust by trial and error or could I adjust and set
to a known litres/minute to get the optimum flow.

You could do either.

How could I find
out what that optimum flow would be - I guess it would be part of the
spec of the boiler?

Look up the power of the boiler, and see if that is input power or
output. If it is input then look up the efficency of it on the SEBUK
database and reduce the actual power by the precentage indicated.

That will give you a number of kW - or 1000s of Joules per second that
the boiler can put into the water. Divide that by 4200 and by the
desired temperature rise, to get the number of kg (i.e. Litres) per sec
the boiler can heat to that temp, then multiply by 60 to get litres per
min. You can then set the flow rate with a bucket and stopwatch.

(personally I would go with the twiddle until about right technique!)

Note that if you set the flow a little too low it does not matter too
much since the water will be hotter, and you just add more cold instead.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In message , John
Rumm writes
Pete wrote:

I have one, and I find it quite difficult to get the flow right to
give optimum amount of hot water.
Would it be worth putting an in-line valve on the cold inlet to the
boiler and then adjusting it such that I could set it to the flow
which would be optimum temperature when taps turned on full? ie it
would limit the flow to a max value which would produce hottest water.

Yes this can work (although obviously you need to adjust the flow
restriction as the groud water warms up in the summer). You may find
the boiler already has a service valve on the cold inlet that you can
partially turn off.

If yes - could I adjust by trial and error or could I adjust and set
to a known litres/minute to get the optimum flow.

You could do either.

How could I find
out what that optimum flow would be - I guess it would be part of the
spec of the boiler?

Look up the power of the boiler, and see if that is input power or
output. If it is input then look up the efficency of it on the SEBUK
database and reduce the actual power by the precentage indicated.

That will give you a number of kW - or 1000s of Joules per second that
the boiler can put into the water. Divide that by 4200 and by the
desired temperature rise, to get the number of kg (i.e. Litres) per sec
the boiler can heat to that temp, then multiply by 60 to get litres per
min. You can then set the flow rate with a bucket and stopwatch.

(personally I would go with the twiddle until about right technique!)

Note that if you set the flow a little too low it does not matter too
much since the water will be hotter, and you just add more cold instead.

Shouldn't be if it's modulating correctly


--
geoff

On Sun, 12 Nov 2006 21:01:01 +0000, John Rumm
wrote:

Pete wrote:

I have one, and I find it quite difficult to get the flow right to
give optimum amount of hot water.

Would it be worth putting an in-line valve on the cold inlet to the
boiler and then adjusting it such that I could set it to the flow
which would be optimum temperature when taps turned on full? ie it
would limit the flow to a max value which would produce hottest water.

Yes this can work (although obviously you need to adjust the flow
restriction as the groud water warms up in the summer). You may find the
boiler already has a service valve on the cold inlet that you can
partially turn off.

If yes - could I adjust by trial and error or could I adjust and set
to a known litres/minute to get the optimum flow.

You could do either.


Excellent - good man, I will give it a go.

raden wrote:

Note that if you set the flow a little too low it does not matter too
much since the water will be hotter, and you just add more cold instead.

Shouldn't be if it's modulating correctly

Depends on if you have set the boilers hot water temp control down low
as well. Most people seem to have it set at 50 - 60 IME... if we are
talking about getting maximum flow at bath temp then the boiler is not
going to be able to achive 50+ anyway in this circumstance.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Sun, 12 Nov 2006 17:20:44 +0000, Pete wrote:

I have one, and I find it quite difficult to get the flow right to
give optimum amount of hot water.

Would it be worth putting an in-line valve on the cold inlet to the
boiler and then adjusting it such that I could set it to the flow
which would be optimum temperature when taps turned on full? ie it
would limit the flow to a max value which would produce hottest water.

If yes - could I adjust by trial and error or could I adjust and set
to a known litres/minute to get the optimum flow. How could I find
out what that optimum flow would be - I guess it would be part of the
spec of the boiler?


The first things to remember is that the DHW temp control on a combi is a
MAXIMUM HW temp. If you draw water faster than it can heat you simply get
more lukewarm water. If this is your case consider yourself lucky, this
situation can be fixed, the opposite problem is a PITA to overcome.

Ideally you want to set things so that turning any HW tap on gives the
right sort of response. This may mean having to restrict the flow
especially on the kitchen sink HW tap. You will probably find that the
bath needs the highest flow/lowest temp so any restriction you add must
not over do it for that tap.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards