Instruction manual

Lower Coil: Two Boiler Installation
Where the lower coil is to be used with a fossil fuel boiler, the
pipework requirements are as per that of a Stainless Indirect single coil
cylinder described earlier in this book. However the electrical
requirements mean the control thermostat inserts into the lower tank stat
pocket to control the boiler input and the limit stat into the upper tank stat
pocket. The two port valve may be installed into either the flow or return
pipework. Wiring of the controls are as per the wiring diagram in this
guide.
DISCHARGE ARRANGEMENT
General guidance is provided by the diagram below, extracted from the
G3 Building Regulation Guidance. This guidance is available as a
free of charge download of the G3 Approved Document from
www.planningportal.gov.uk. The discharge from both the Temperature
relief and expansion relief valves can be joined together via a 15mm end
feed Tee.
It is important that any discharge water does not collect in this pipe-
work and can run freely to the tundish. The tundish should be mounted in
a vertical and visible position located in the same space as the unvented
hot water storage system and be fitted as close as possible and within
500mm of the safety device e.g. the temperature relief valve. The
discharge pipe-work from the tundish must be routed in accordance
with Part G3 of the Building Regulations.
The discharge pipes and tundish should be installed in a visible location
away from any electrical devices, should terminate in a safe place where
there is no risk to persons in the vicinity of the discharge, be of metal
and:
a) Be at least one pipe size larger than the nominal outlet size of the
safety device unless its total equivalent hydraulic resistance exceeds
that of a straight pipe 9m long i.e. discharge pipes between 9m
and 18m equivalent resistance length should be at least two sizes
larger than the nominal outlet size of the safety device, between 18
and 27m at least 3 sizes larger, and so on. Bends must be taken
into account in calculating the flow resistance. An alternative
approach for sizing discharge pipes would be to follow BS6700
Specification for design installation, testing and maintenance of
services supplying water for domestic use within buildings and
their curtilages.
b) Have a vertical section of pipe at least 300mm long, below the
tundish before any elbows or bends in the pipework.
c) Be installed with a continuous fall.
d) It is preferable for the discharge to be visible at both the tundish and
the final point of discharge but where this is not possible or practically
difficult there should be clear visibility at one or other of these
locations.
Examples of acceptable discharge arrangements are:
1. Ideally below the fixed grating and above the water seal in a
trapped gulley.
2. Downward discharges at a low level; i.e. up to 100mm above
external surfaces such as car parks, hard standings, grassed
areas etc. are acceptable providing that where children play or
otherwise come into contact with discharges, a wire cage or
similar guard is positioned to prevent contact whilst
maintaining visibility.
3. Discharges at a high level; e.g. in to metal hopper and metal down
pipe with the end of the discharge pipe clearly visible tundish
visible or not) or onto a roof capable of withstanding high temperature
discharges of water and 3m from any plastic guttering systems
that would collect such discharges (tundish available).
4. Where a single pipe serves a number of discharges, such as in blocks
of flats, the number served should be limited to not more than 6
systems so that any installation can be traced reasonably easily. The
single common discharge pipe should be at least one pipe size larger
than the largest individual discharge pipe to be connected. If unvented
hot water storage systems are installed where discharges from
safety devices may not be apparent i.e. in dwellings occupied by
blind, infirm or disabled people, consideration should be given
to the installation of an electronically operated device to warn
when discharge takes place.
Safety Device
(eg: Temperature
Relief Valve)
Metal Discharge Pipe From
Temperature Relief Valve To Tundish
500mm Max
Tundish
300mm Min
Diagram of a typical discharge pipe
arrangement (extract from Building
Regulation G3)
Note: The discharge will consist
of scalding water and steam.
Asphalt, roofing felt and non-metallic
rainwater goods may be damaged
by such discharges.
Note: It is not acceptable to
discharge straight into a soil pipe.
Discharge Below
Fixed Grating
Trapped
Gulley
Metal Discharge Pipe From
Tundish, With Continuous Fall