10
8. OSO Fault Finding Guide
Alternative Discharge
Discharge pipes should be in metal and
dedicated to the unvented cylinder. The pipe
should have a continuous fall and should terminate
in a safe and visible place.
Downward discharges at low level, i.e. up to 100 mm above
external surfaces such as car parks, hard standings, grassed
areas etc. are acceptable providing that where children may
play or otherwise come into contact with discharges,
a wire cage or similar guard is positioned to prevent
contact, whilst maintaining visibility.
Discharge at high level, i.e. into a 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
3 m from any plastics guttering system that would collect such discharges
(tundish visible).
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 discharging can be traced reasonably easily. The single common dis
-
charge pipe should be at least one pipe size larger than the largest individual discharge pipe to be connected. For further
information contact your Building Control Office.
Important - note:
Disconnect electrical supply before removing any electrical equipment covers.
FAULT
POSSIBLE CAUSE
SOLUTION
No water flow from hot taps.
1. Mains supply off.
1. Check and open stopcock.
2. Strainer blocked.
2. Turn off water supply. Remove strainer and clean (see
Servicing Procedure page 10).
Water from hot taps is cold.
1. Immersion heaters not switched on.
1. Check and switch on.
2. Immersion heater thermal cut-out has operated
2. Check and reset button (see thermostat diagram page 8
and safety cut-out on page 5 of installation manual).
3. Programmer set to central heating or not switched on.
3. Check and set to hot water.
4. Boiler not working.
4. Check boiler operation. If fault suspected consult installer
or boiler manufacturer.
5. Cylinder thermal cut-out has operated (indirect units only). 5. As at No. 2.
6. Motorised valve not operating correctly.
6. Check wiring and/or plumbing connections to motorised
valve (see pages 6 - 9 of the installation manual).
Intermittent water discharge.
1. Reduced expansion vessel charge.
1. Follow instruction page 10: “Intermittent or slow water
discharge from tundish”.
Continous water discharge.
1. Thermal control failure (Note: Water will be hot).
1. Switch off power to immersion heater(s) and boiler supply
to the unit. When discharge has stopped, check thermal
controls, replace if faulty. Contact a competent person.
2. Cold water inlet Pressure Reducing Valve not working.
2. Check pressure from valve, if greater than 3 bar replace
(see page 10 of installation manual).
3. Temperature and pressure relief valve faulty.
3. Drain 10 litres from cylinder and replace valve.
4. Expansion relief valve not working properly.
4. Check and replace if faulty (see page 6 of installation manual).
Minimum size of
Maximum resistance allowed,
Minimum size of
discharge pipe D2* expressed as a lenght of straight Resistance created by
Valve outlet size discharge pipe D1* from tundish
pipe (i.e. no elbows or bends)
each elbow or bend
22 mm
up to 9 m
0.8 m
G1/2
15 mm
28 mm
up to 18 m
1.0 m
35 mm
up to 27 m
1.4 m
28 mm
up to 9 m
1.0 m
G3/4
22 mm
35 mm
up to 18 m
1.4 m
42 mm
up to 27 m
1.7 m
35 mm
up to 9 m
1.4 m
G1
28 mm
42 mm
up to 18 m
1.7 m
54 mm
up to 27 m
2.3 m
Table D
