Fault finding Flashcards

1
Q

Give FOUR reasons why spillage from a gas appliance may occur

A
  • Blocked flue.
  • Lack of ventilation.
  • Too many bends.
  • Disturbed air at cowl.
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2
Q

A fault has developed on a gas-fired, electronic continuous-flow water heater. When the
water tap is turned on, the appliance starts and the gas ignites, but the appliance shuts
down after a few seconds. An error code is displayed which indicates failed ignition.
Give FOUR reasons for this fault to occur.

A
  • Low gas pressure.
  • Faulty/dirty flame sensor probe or lead.
  • Partially blocked burner or heat exchanger.
  • Faulty earth circuit.
  • PCB Fault.
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3
Q

A fault has developed on a gas oven. After the oven has been running for 20 minutes, it shuts the
gas off and must be manually restarted.
Give THREE likely causes for this to occur.

A
  • The thermocouple is too far from the flame.
  • The oven by-pass is set incorrectly.
  • The thermostat is faulty.
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4
Q

Often when a gas storage water heater is first started the sound of water dripping onto the
burner is heard.
(i) Explain how this water is produced.

A

The water comes from the flue gases cooling while in the flue and condensing into water, running down the baffle to drip on the burner.

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5
Q

Explain why the dripping occurs more at different times.

A

It occurs more when the water heater is cold because the cold sides of the tank cool
the flue gases faster than normal.

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6
Q

A boiler fitted with a package burner operates on natural gas.
(a) State THREE ‘conditions’ that must be met in order to perform an accurate flue gas analysis

A
  • Appliance has reached equilibrium or steady state operation.
  • Burner is operating at full fire.
  • Readings are taken in the centre of the flow of products of combustion.
  • Measurements are taken as close as possible to the appliance.
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7
Q

Give THREE flue gas (measurement’s) that are needed to calculate the boiler efficiency flue
gas analysis

A
  • Flue gas temperature.
  • Carbon dioxide to air ratio.
  • Oxygen percentage.
  • Carbon monoxide reading
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8
Q

List in order TEN steps in the operational sequence of a gas-fired electronic continuous flow water heater.

A

1 Hot water tap is opened.
2 The Water Flow Sensor sends a pulse signal to the PCB.
3 Fan completes a pre purge.
4 The igniter starts sparking.
5 Gas Inlet Solenoid Valves open.
6 The Gas Flow Regulating Valve allows adequate gas for ignition.
7 Gas ignites at the Burner.
8 Flame sensor detects burner flame.
9 The PCB adjusts the hot water temperature by opening and closing the Gas Solenoid Valves
Hot tap is closed.
10 The pulse signal from the Water Flow Sensor stops.

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