Hamworthy Purewell Variheat mk2 70c Installation, Commissioning And Servicing Instructions page 54

E1.4 Open Vent and Cold Feed Pipe.
Every boiler or group of boilers should have an open vent pipe and cold feed pipe installed between the boiler and
the first water isolating valve. The minimum bore (mm) of these pipes per installation is shown in the table. The
vent pipe must rise continually, any valve fitted between a boiler and the open vent pipe for maintenance
purposes shall be of the 3 way type such that when closed to the vent pipe the boiler will be open to atmosphere.
The vent pipe shall be protected against freezing where this might occur. See BS 6644 for detailed information on
Open Vent and Cold Feed Pipes.
E1.5 Altitude Gauge (Water Pressure Gauge)
Every boiler or group of boilers should be provided with an altitude gauge complete with isolating valve. See
Figure E1.2 for typical position.
E1.6 Thermometer
A thermometer complete with pocket should be fitted in the pipework to indicate water flow temperature. See
Figure E1.2 for typical position.
E1.7 Drain Valves
Each boiler is fitted with a 15mm NB drain valve in the boiler return to drain the boiler only. The heating system in
total should have drain valves as recommended by BS 6644. See Figure E1.2 for typical position.
E1.8 Circulating Pump
One or more circulating pumps will be required to circulate water around the boilers and heating system. The
pump should be sited to facilitate servicing. It is important that when Purewell Variheat mk2 boilers are used to
replace boilers on an existing system, the pumps should be checked for performance against the new boiler
waterside pressure loss to ensure that the minimum flow rate can be obtained. It is also important that the existing
system be flushed through twice to remove any loose matter which may have accumulated. If in any doubt
regarding the cleanliness of the system, a coarse filter should be fitted in the return pipework to the boilers.
If boiler / system pump(s) are not controlled by the boiler, a pump overrun (not Hamworthy Heating Ltd supply)
should be fitted which must run for a minimum of 5 minutes on shutdown of the last boiler.
E1.9 Minimum Water Flow Rates
Minimum water flow rates are shown in table at beginning of Appendix E. These flow rates should be maintained
through the boiler at all times whilst the boiler is firing. If the water flow rate is allowed to fall below the minimum
the boiler heat exchanger could fail due to the resultant scale formation. Particular attention should be paid to the
restriction of external flow circuits during periods of low heat demand.
E1.10 Waterside Pressure Drop
The waterside hydraulic resistance (Pressure drop) is given in table E1 at beginning of Appendix E.
E1.11 Water Flow Controls
Any external mixing valve / shunt pump or similar controls MUST always ensure that the minimum water flow rate
as given in table at beginning of Appendix E is maintained. If there is any doubt relating to site flow conditions it is
suggested that a flow switch is fitted. The flow switch should be connected such that the boiler will shut down if
insufficient flow occurs.
E1.12 Frost Protection
Consideration should be given to fitting a frost thermostat set at approximately 4°C
E1.13 Unvented Systems
Refer to Figure E1.2 for typical layout of an unvented (Pressurised) Hot Water System. For system design refer
to BS 7074 Part 2. In order to correctly size a pressurisation unit for any heating system the following parameters
are required.
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HAMWORTHY HEATING LTD PUREWELL Variheat mk2 218612 A03