Fault Finding; Replacement Of Parts - Benchmark Metropolis DGT 25 BF Installation And Servicing Instrucnion

5

FAULT FINDING

If an electrical fault occurs on the appliance
ENG
the preliminary electrical system checks
must be carried out first.
IT
When any service or replacement of elec-
trical components which has required the
breaking and re-making of electrical con-
ES
nections has taken place, the following tests
must be repeated:
– earth continuity;
– short circuit;
– polarity;
– resistance to earth.
5. 1 EARTH CONTINUITY CHECK
Appliances must be electrically disconnect-
ed, meter set on Ω (ohm) x 1 scale and
adjust zero if necessary. Tests leads from
any appliance earth point (e.g. inside control
box) see wiring diagrams (section 7) to
earth pin on plug. Resistance should be less
than 1 Ω (ohm). If the resistance is greater
than 1 Ω (ohm) check all earth wires for
continuity and all contacts are clean and
tight. If the resistance to earth is still
greater than 1 Ω (ohm) then this should be
investigated futher.
6

REPLACEMENT OF PARTS

6. 1 EXPANSION VESSEL
- Isolate the boilers power supply.
- Remove the boiler cover, see 4.3.
- Close the flow and return isolation valves.
- Drain the boiler using the fitted drain
vent, see fig 15.
- Protect the control board from acciden-
tal spillage of water.
- Disconnect the expansion pipe.
- Remove the securing screw at the top of
the vessel.
- Lift out the vessel.
- Before fitting the new vessel, check the
charge pressure, see TABLE 4.
- Refit in reverse order.
6.2 IGNITION / IONISATION
ELECTRODE
- Isolate the boilers power supply.
- Remove the boiler cover, see 4.3.
- Remove the sealed chamber cover.
- Disconnect the electrode.
- Remove the securing screw and remove
the electrode.
- Refit in reverse order, checking that the
spark gap is as shown in Fig 21.
6.3 BURNER REMOVAL
- Isolate the boilers power supply.
28
5.2 SHORT CIRCUIT CHECK
Switches turned FULL ON - meter set on Ω
(ohms) x 1 scale. Test leads from L to N on
appliance terminal block, if meter reads 0
then there is a short circuit.
Meter set on Ω (ohm) x 100 scale. Repeat
it with leads from L to E. If meter reads less
than infinity (∞) there is a fault.
NOTE: Should it be found that the fuse has
failed but no fault is indicated, a detailed
continuity check (i.e. by disconnecting and
checking each component) is required to
trace the faulty component.
It is possible that a fault could occur as a
result of local burning/arcing but no fault
could be found under test. However, a
detailed visual inspection should reveal
evidence of burning around the fault.
5.3 POLARITY CHECK
Appliance reconnected to mains supply and
meter set on 300 V ac scale. Test at appli-
ance terminal block.
– Test leads from L to N meter reads
- Remove the boiler cover, see 4.3.
- Isolate the gas supply.
- Remove the sealed chamber cover.
- Remove the burner cover.
- Disconnect the ignition electrode.
- Disconnect the gas connection to the
burner.
- Remove the burner securing nut.
- Carefully lift out the burner assembly.
- Replace in reverse order, replacing
gaskets as required.
6.4 FAN
- Isolate the boilers power supply.
- Remove the boiler cover, see 4.3.
- Remove the sealed chamber cover.
- Disconnect the electrical connections
from the fan.
- Disconnect the venture pipe.
- Remove the three fixing screws.
- Remove the fan.
- Replace in reverse order, ensuring that
the fan to flue seal is undamaged and
correctly positioned.
6.5 BITHERMAL HEAT EXCHANGER
- Isolate the boilers power supply
- Remove the boiler cover, see 4.3.
- Close the flow and return isolation valves.
- Drain the boiler using the fitted drain
approx.: 240 V ac.
– Test leads from L to E " " meter reads
approx. 240 V ac.
– Test leads from N to E " " meter reads
from 0 to 15 V ac.
5.4 RESISTANCE TO EARTH CHECK
Appliance must be disconnected from main
supply and meter on Ω (ohm) x 100 scale.
All switches including thermostat on test
leads from L to E - if meter reads other than
infinity (∞) there is a fault which should be
isolated.
A detailed continuity check is required to
trace the faulty component.
IMPORTANT:
These series of checks are the first elec-
trical checks to be carried out during a
fault finding procedure. On completion
of the service/fault finding task which
has required the breaking and remaking
of electrical connections then the
checks 5. 1 Earth continuity, 5.3 Polarity
and 5.4 Resistance to earth must be
repeated.
vent, see fig 15.
- Remove the sealed chamber cover.
- Remove the fan as see 6.4.
- Remove the burner cover.
- Disconnect the heating sensor
- Remove the four pipe securing clips
- Carefully lift out the heat exchanger.
- Transfer the heating sensor to the new
heat exchanger
- Refit in reverse order.
6.6 HEATING SENSOR (SM1/SM2)
- Isolate the boilers power supply.
- Remove the boiler cover, see 4.3.
- Remove the sealed chamber cover.
- Disconnect the electrical connections
from the heating sensor.
- Unclip the sensor from the heat exchan-
ger.
- Refit in reverse order.
6.7 AIR PRESSURE SWITCH
- Isolate the boilers power supply.
- Remove the boiler cover, see 4.3.
- Remove the sealed chamber cover.
- Note the positions of the electrical con-
nections to the air pressure switch and
remove.
- Note the position of the sensing pipe and
disconnect.