JimGC wrote:

Bear with me a moment ... I'm shocked at the cost of running
my small flat's combi boiler compared to my previous
terraced house boiler which had a hot water tank. The cost
has doubled (3bd house HW/CH with 4 occupants was £360pa
over the year, 1 bd flat combi HW/CH with 1 occupant ran up
£60 in December alone!) The flat is fairly modern (1982) in
good condition, and I have the water/ch on from 6-9am and
from 4-11pm, turning it off when CH gets too hot. Dec. is
the worst month of the year measure usage, but even if it
all drops 50% for the rest of the year, it's still too high
for my liking.

Given that you currently have the heating on, and many months of the
year you don't, I would expect to the difference between worst and best
months to be closer to 90% (i.e. most hours of the day you won't be
using any hot water and hence the boiler will be using no gas at all).

So a sample of costs taken from one month like this tell you nothing
really.

The reason for posting here is that I have already asked
about the inability of the boiler to provide a constant flow
of hot water. (CH seems to be very hot whenever it's on
whatever the thermostat on the boiler is set to).

That sounds like you do not have full thermostatic control in place
(i.e. room stat, and thermostatic radiator valves on all rads (except
the one in the room with the room stat).

Is it possible that the boiler has faulty thermostats and is
failing to provide constant hot water, but also using way

What do you mean by failing to provide constant hot water exactly? (i.e.
it works when the tap is first turned on, but the goes completely cold,
or does it run warm but not as hot as when you started etc).

There are several issues he

Firstly the thermostat for hot water in a combi just sets the upper
limit on the temperature. i.e. if you are using hot water it should not
supply it at a temperature exceeding that set on the stat.

The lower limit is usually set by the laws of physics. The boiler can
provide heat at a rate governed by its basic design (tell us the
make/model number and we can give you more info). The more powerful the
boiler, the more water it can heat in a given time. Hence if you ask for
a small flow of hot water it will supply it at a temperature governed by
the HW stat. As you turn the tap on more, you reach the limit of the
boilers power where even running flat out it can still not heat the
water to the stat temperature and the temperature of the water will
begin to fall. Select a high enough flow rate and it will not be able to
heat it enough to get it to a usable temperature.

There is yet one more issue, that there can be times when you are asking
for a small amount of hot water that the boiler is producing heat too
fast such that it would end up exceeding the stat temperature an hence
it has to turn off its burner. Some combis also use a relatively
insensitive flow switch which requires a good flow of water to be
requested before they will switch to hot water mode.

The moral of the story is that you need to choose your combi carefully
since there are lots of crap combis on the market, with too little
power, and lots of quirks when running. Alas if you landlord made the
choice for you you can probably guess what end of the market he went for!

too much gas to feed the CH? Or am I just paying the price
for having this kind of boiler? Is it possible that I'm

All things being equal with the boilers efficiency, there is no reason
for a combi to be less efficient than a system boiler with a hot water
cylinder. In fact it will tend to be more efficient since there is less
risk of you loosing energy from the stored hot water.

Having said that, any boiler can be run inefficiently with poor (or no)
control systems. You can also get a large variation in basic efficiency
between different boilers (i.e. the worst will give perhaps 70p worth of
heat for every pounds worth of gas, the best will give over 96p worth of
heat).

using the combi boiler in the wrong way, and that these
fixed timing settings are not appropriate to combis?

Could well be.

I plan to get a CORGI man in early in the new year to give
it the once over, landlord or not!

May help.

--
Cheers,

John.

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