All instant water heating appliances suffer from this. Our instant shower
is usually set around the four or five mark on the temperature gauge in the
summer time, but it is now being set to either six or seven. We also notice
the flow dropping when we set the gauge to a higher temperature setting,
because that's how these things work. You slow down the flow rate to keep
the water in the boiler (heater tank) a bit longer so the heating element
(exchanger) has time to heat it up to the temperature you need.
You could fit a hot water storage tank dedicated to the shower and fed from
a loop off the central heating system.
1) Adjust a tap so it fills a pint bottle in 6 seconds...............is the
water now hot?
2) Also look in the instructions and find the spec. of the boiler usually
quoted to give a flow rate against temp. rise (eg 2.2 gallons/min @ 35' C
Subsitute the figures for your boiler, for the ones I have us below.
Note the temp. of the incoming cold water (eg 12'C)
Slow the hot tap down to give a flow rate of 2.2 gallons per minute
The hot water should now be 12'C+35'C = 47'C
Hi Skip what you say is probably correct, but I didn't have to adjust the
flow at the tap previously, even if I had the hot tap on full, it would be
only flow at a normal speed with piping hot water.
Maybe the input cold pressure has increased and I have to restrict it??.
The water going into the boiler is now colder than it was in the summer
months, so the boiler needs more time to heat the water. If the flow rate
stays the same and the incoming water gets colder, then the boiler will not
heat it to the same temperature in the same time as it used to.
Fill your kettle with cold water from the tap. Switch it on and time how
long it take to boil.
Now fill your kettle with water that has been stored in your fridge for a
day. Switch it on again and time how long it takes to boil.
You should notice a difference in the times, with the colder water from the
fridge taking longer to come to the boil than the water straight from your
The same thing is happening with boiler.
I have had a good look at the boiler tonight, there are two thermistors at
the top of the boiler, on the pipes by the top of the heater thing by the
flames, behind the big cover.
The only other one is attached to the hot water exit pipe at the bottom,
this is what I think Boshe are referring to.
I have measured the resistance across this component, out of circuit. When
cold attached to the pipe, it reads 14K, when it is hot it reads 4K. Is this
normal?? The markings on it are 6655 9003 3-5
Any ideas appreciated
Having just read this, the discussion seems to be going round in circles.
The simple problem seems to be that the hotwater is now flowing much faster,
and so comes out of the tap much cooler.
[So don't turn the tap on full!]
There are two different possible reasons which have been suggested for the
change in water flow:
(1) There is a flow control valve in the boiler which restricts the flow of
water through the boiler to allow it to be heated to the set temperature.
This is now not working.
(2) The rate of flow is not regulated by the boiler. Therefore something has
changed in the mains cold feed to the boiler, resulting in a faster flow
rate than before which is now too fast for the boiler to heat the water
properly when the bath tap is fully open.
Attempted diagnosis seems pointless until you establish which of these two
conditions is true.
The fix to (2) is obvious!
P.S. (3) The OP has neglected to mention that the bath taps have been
Taps not been changed, but there is a flat bladed screw on the cold water
input pipe, this has been switched off and on in the past, it turns 45
degrees, maybe I should turn this to restrict the flow???
I would like to know if the Worcester 24 CDI does have a flow restriction
Thanks for all your help, I will have a fiddle with the little screw thing
to restrict it.
The valve you're describing is called a service valve, and the slot is
connected to a ball shaped (spherical) closer inside the valve. The slot
will be at a right angle with the direction of the pipe to be fully off
(closed) and running in the same line as the direction of the pipe to fully
|_| = Closed (off)
| | | = Open (on)
If this is on the cold feed to the boiler then this may explain all.
Turning it slowly whilst an assistant hold a hand under the bath tap may
allow you to adjust it to roughly where it was before.
Once you have adjusted the mains cold input to the boiler, I guess you
should then measure the flow rate of the hot water to see if it is
sufficient for the proposed thermostatic shower. You could also check that
this is the expected flow rate of hot water through the boiler.
As suggested elsewhere, if you don't have sufficient flow then you will need
some sort of thermal store and a pump to supply pressurised hot water to the
P.S. It is where you replace a traditional boiler and hot water tank with a
combi boiler to reduce complexity and save space, then add on a thermal
store because you don't have enough flow for your shower(s), that I start to
lose the plot :-)
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