"ChrisJ" wrote in message
...

"Toby" wrote in message
...
As stated about the Worcester Greenstar Condensing Combi -
"Key features of the Greenstar include the pre-heated domestic hot water
heat exchanger. After the store has reached temperature hot water is
delivered instantly to the outlet being operated. The temperature and
frequency of the recharge of the store may be pre-set. Modulating
central
heating and domestic hot water outputs, combined with separate consumer
controls, also mean that comfortable temperature levels for both can be
set
independently of each other."

Does that meant that for short runs the boiler won't fire up but will use
water in the small tank and if you run the tap for longer then the bolier
kicks in?

EG I rinse a mug out, 5-10 seconds of water, boiler doesn't fire up HW
comes from mini storage tank.
I wash my hands water comes from hot water store until its level drops to
a
certain level then boiler kicks in and supplies water to tap and refils
storage tank
I have a shower water comes from hot water store until its level drops to
a
certain level then boiler kicks in and supplies water to shower and
refills
storage tank when I've finished my shower.

I don't want to be heating a whole load of water I'll not be using or I'll
be in the same state as the house is now with a boiler and a hot water
tank.

Any one suggest a website where I can find out more?

Chris J

The tanks are usually well insulated and small. Some combi's have stay warm
heat exchangers. The boiler keeps the domestic hot water heat exchanger to
certain temp, so when hot water is drawn off there is no lag. The Greenstar
has a pre-heated domestic hot water heat exchanger. This is usually user
switchable, so you don't keep the heat exchanger hot when away for 6 weeks.

The lag is mainly because of the priming affect of the boilers fanned
controls. On start up, it has to purge the burner box with fresh air by
running the fan and determine if the fan is running, then the gas valve
switches in. This takes a little time.

The crappy Ravenheat condensing combi reduces the lag time by having the fan
continually run, so the gas valve switches in as soon as there is flow. This
costs more in electricity to needlessly run the fan and it also extracts
heat from the heat exchanger dumping it to the outside air. In sub-zero
temperatures freezing air is being drawing in so the frost controls cut in
to protect the heat exchanger and fire the burner, again wasting fuel. Best
avoided.



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