Fault finding

Question 1

Give FOUR reasons why spillage from a gas appliance may occur

Answer 1

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

Question 2

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.

Answer 2

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

Question 3

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.

Answer 3

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

Question 4

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.

Answer 4

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.

Question 5

Explain why the dripping occurs more at different times.

Answer 5

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

Question 6

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

Answer 6

• 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.

Question 7

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

Answer 7

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

Question 8

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

Answer 8

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.