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4.7 - DOMESTIC HEATING & HOT WATER - REGULATIONS & GUIDELINES
When the heating system is up to full working
temperature, if the pointer on the pressure gauge
should enter the red zone (between 2.5 - 4 bar
pressure), it is likely that:
(a) The total system water content is greater than
that calculated and if additional expansion
vessel has been fitted it should be replaced with
a larger unit;
or if only the integral boiler expansion vessel
is used, then an additional expansion vessel is
required.
(b) The static head may be higher than calculated.In
this case it is necessary to re-measure the static
head and revise the expansion vessel air charge
pressure.
(c) The expansion vessel is the incorrect size or the
air charge pressure is incorrect.
Refer to BS 7074 Part 1 and BS 5449 Part 1
for further information.
EXAMPLE: using the table on this page:
If total water content of system is - 150 litres
and initial system pressure required is - 1.0 bar
then vessel volume required is - 16.3 litres
[from above table]
The vessel supplied with boiler is - 12.0 litres
therefore an additional vessel of - 4.3 litres
is required
(minimum)
(For this system of 150 litres - total water volume)
The nearest available stock size for additional vessel
required, at 1 bar initial system pressure (taken from
above table) is 5 litres.
It is emphasised that the installer should be fully
acquainted with sealed system installation and
operation, calculation of total system water volume,
determining of initial system pressure required and
calculation of any additional expansion vessel volume
required. The warranty is void if the boiler is installed
in a system with insufficient expansions.
N.B. Ensure that all expansion vessels in the same
system are set at equal air charge pressures.
Safety Valve Setting 3 bar
Initial System Pressure 0.5 bar 1.0 bar 1.5 bar
Total Water Content TOTAL VESSEL
of System VOLUME **
Litres Litres Litres Litres
25 2.1 2.7 3.9
50 4.2 5.4 7.8
75 6.3 8.2 11.7
100 8.3 10.9 15.6
125 10.4 13.6 19.5
150 12.5 ->[16.3]<- 23.4
175 14.7 19.1 27.2
200 16.7 21.8 31.2
225 18.7 24.5 35.1
250 20.8 27.2 39.0
FOR FURTHER INFORMATION CONSULT
APPROPRIATE TRAINING MANUALS
AND BS 7074 PART 1, BS 5449 PART 1, ETC.
* * When calculating the size of any additional
expansion vessel, remember to deduct
the boiler expansion vessel volume of 12 litres
from the calculated total system vessel volume
required, as given in the above table.
EXPANSION VESSEL AND SYSTEM
REQUIREMENTS
DOMESTIC HOT WATER CIRCUITS
The final 600 mm mains water supply should be of
copper tube to BS 2871 Part 1. Ensure that any capillary
fittings used are of a lead free solder variety.
For user comfort, the mains pressure at the taps
should be between 1 and 5 bar. If it exceeds this, it is
advisable to fit a pressure reducing valve adjusted
to reduce pressure to an acceptable level within the
above range. It may be advisable to discuss this with
the householder.
Where long hot water supply pipe runs are used, these
should be insulated to prevent rapid cooling of residual
hot water after draw off is completed.
If the boiler is fitted in a hard water area, check that the
hardness does not exceed 150 p.p.m., by testing with a
standard test strip. Immerse test strip in flowing tap
water for one second. Shake off excess water. Check
strip after approximately fifteen seconds. If three or
more zones have changed colour, the water hardness is
over 150 p.p.m.(read instructions on test strip package).
Fitting of an in line scale inhibitor is then necessary.
Failure to check water hardness and fit appropriate
water softening equipment will result in scale build
up and consequent reduction in water heating
performance. Check with local Water Authority if in
doubt.
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