9
mostat settings to ‘smart -’ (if you require water
to remain at 70 an additional potable expan-
sion vessel is required) A secondary return can
be connected via the expansion vessel connec-
tion to the combination valve. Remove the hose,
connect a short length of 15 mm copper tube, fit
a T piece, connect in the secondary return and
reconnect the expansion vessel hose to the re-
maining T piece outlet. An additional expan-
sion vessel will be required if the secondary re-
turn ‘loop’ exceeds 10% of the cylinder capacity.
1 metre of 22 mm pipe holds approximately 1/3
litre of water. 15 mm pipes carry approximately
half that volume. Secondary return must be
pumped by a bronze pump and fitted with non
return valves to ensure correct direction of flow.
2.21 Discharge pipe
Connect the tundish outlet to the discharge pipe.
Install the tundish in a vertical position within a
maximum of 500 mm from the Temperature and
Pressure Relief Valve drain connection. Ensure
the expansion relief pipework discharges through
the tundish. Tundish pipework must be 22 mm
with a minimum vertical length of 300 mm below
tundish. Maximum permitted length of 22 mm
pipework is 9 m.
Each bend or elbow is equivalent to 0.8 m of
pipework. All pipework must have continous fall
and discharge in a safe, visible position. If any
doubt, refer to Building Regulation G3. Discharge
pipe must be dedicated to the cylinder and must
not be used for any other purpose.
3. COMMISSIONING
3.1 Commissioning and filling
1. Check all connections for tightness. Open hot
water tap furthest away from the OSO water
heater.
2. Open the mains stop cock to fill the water
heater. When water flows evenly from tap, al-
low to run for a few minutes to flush through
any dirt, swarf or residue, then close the tap.
Open successive hot taps to purge any re-
maining air.
3. Check all water connections for leaks and rec-
tify if necessary.
4. Manually operate Expansion relief valve (6)
(see illustration on previous page) to ensure
free water flow through discharge pipe by
turning knob counter-clockwise. To close
continue to turn counter-clockwise until the
valve shuts.
5. Manually operate Temperature and Pressure
Relief Valve (8) (see illustration on previous
page) to ensure free water flows through dis-
charge pipe (Turn knob counter-clockwise).
6. Switch electrical power on.
7. Replace the cylinder lid – this is important as
the lid prevents heat loss from the cylinder
and combination valve, conserving valuable
energy. Do not place heavy objects on the lid.
3.2 Draining
Switch off the electrical power (important to avoid
damage to element). Turn off the cold water sup-
ply valve. Open hot water tap. Open drain at base
of cylinder using a 6 mm hex key. The unit will
drain. Draining process may be speeded up by
opening the temperature and pressure relief valve.
An internal ø18 mm hose can be applied to bot-
tom drain cock to lead the water to a gully, sink
or similar.
3.3 System flushing
System flushing will not be necessary under nor-
mal circumstances as the line strainer will prevent
ingress of foreign materials, however if flushing is
required, run at least 50 litres of water from the
cylinder at the highest possible flowrate. Close the
taps and follow draining procedure above.