Just had a new combi boiler fitted from a previous hot water tank
installation.We have a Ferroli Maxima 35c boiler which I think is high flow.

Problem is when toilet is flushed or water is needed by the washing machine,
it stops cold water coming out of the bathroom taps. I've sort of read that
this type of behaviour (reduced flow) is expected with combi systems but is
it normally that bad (ie. flush toilet and no cold water flow to sink in
bathroom even if nothing else on).

Secondly, is there a way to restrict the flow rate into toilets/appliances
so at least there's some pressure into the taps which is where you would
want the instant access?

"fonzy" wrote in message
...
Just had a new combi boiler fitted from a previous hot water tank
installation.We have a Ferroli Maxima 35c boiler which I think is high
flow.

Problem is when toilet is flushed or water is needed by the washing
machine,
it stops cold water coming out of the bathroom taps. I've sort of read
that
this type of behaviour (reduced flow) is expected with combi systems but
is
it normally that bad (ie. flush toilet and no cold water flow to sink in
bathroom even if nothing else on).

Secondly, is there a way to restrict the flow rate into toilets/appliances
so at least there's some pressure into the taps which is where you would
want the instant access?

Combi's do not reduce flow. If the mains pipe is fine then usually all is
OK. When you have problems It is best to:

1. Replace the mains stop cock with a full bore cock.
2. Run 22m to the combi only.
3. After the stop cock tee off and run a cold pipe to the cold only taps.
4. The cold pipe for the shower take from the cold supply just before the
combi.
5. In-line isolation taps on the cold taps and hot taps to dishwasher &
w/machine. Throttle these back to suit.

What you have done is have the combi take the line of least restistance is
the cold water flow from the street.

If still problems, then consider having the mains pipe replaced back to the
street with large bore plastic pipe.

fonzy wrote:

Just had a new combi boiler fitted from a previous hot water tank
installation.We have a Ferroli Maxima 35c boiler which I think is high flow.

Problem is when toilet is flushed or water is needed by the washing machine,
it stops cold water coming out of the bathroom taps. I've sort of read that

Is this only when the combi is suppling hot water, or at any time?

this type of behaviour (reduced flow) is expected with combi systems but is
it normally that bad (ie. flush toilet and no cold water flow to sink in
bathroom even if nothing else on).

The reduced flow that you often hear about is typically a reduction in
flow of *hot* water when compared to a stored water system. With no hot
water being used, the cold flow rate to the rest of the house should be
the same.

With the hot running, your combi will be able to heat the hot water to a
usable bath or shower temperature at a rate of approx 10 - 14 L/min (the
colder the ground water coming into the house the lower the rate).
There ought to be enough mains cold water flow rate to supply this and
at least another cold tap at the same time.

If not then your rising main is not adequate for the setup you currently
have. (Plus the person who fitted the combi without checking the
flowrate first was a cowboy!)

A quick thing to check, make sure the main stopcock is turned full on.

Secondly, is there a way to restrict the flow rate into toilets/appliances
so at least there's some pressure into the taps which is where you would
want the instant access?

You can fit a service valve before each of them and then partially turn
it off to limit the flow rate.

You may also also improve matters by improving the supply from the main.
This can be as simple as fitting a full bore valve in place of the more
typical stopcock, or as extream as replacing the whole main back to the
street!)

--
Cheers,

John.

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"fonzy" wrote in message
...
Just had a new combi boiler fitted from a previous hot water tank
installation.We have a Ferroli Maxima 35c boiler which I think is high
flow.

Problem is when toilet is flushed or water is needed by the washing
machine,
it stops cold water coming out of the bathroom taps. I've sort of read
that
this type of behaviour (reduced flow) is expected with combi systems but
is
it normally that bad (ie. flush toilet and no cold water flow to sink in
bathroom even if nothing else on).

What was the flow rate and pressure before the combi was installed? If you
used stored hot & cold water beforehand this can mask a very poor flow rate
from the mains. If you've got 13mm mains into the house then IME you simply
can't get enough water through that pipe to reliably meet demand in anything
other than a small house/flat with no more than two people living there.
Your case does sound extreme though, if you're lucky it could just be
something simple like the mains stopcock isn't turned on fully. If you're
unlucky it could cost a small fortune putting larger bore pipe out to the
mains in the street.

Go back to your plumber, ask him what the flow rate was before the boiler
was fitted, on what basis did he feel it was adequate and why a combi was
the best solution for your needs. When you get up off the floor and after
the black eye's faded you'll probably find he fitted the combi cos he could
then justify charging for a pressure flush and additional pipework yet the
wiring's so simple it didn't tax his limited electrical skills too much.

Rgds

Andy R