Fault Guide : Smiths Combustion Heaters

FAULT POSSIBLE CAUSE REMEDY
Heater will not start a) heater cable disconnected Examine plug and socket contacts and insert plug firmly into socket
  b) fuse blown Test for earth fault and replace fuse
  c) saloon thermostat operated (auto types only) Check saloon temperature and test by shorting out saloon thermostat
  d) control panel or wiring Change panel and test on test rig
  e) motor o/ circuit Change heater. If within 4 months of installation test on rig wires 8/9
  f) excess heat thermostat or micro switch on electronic type o/ circuit Ensure battery voltage at 20v minimum. Replace heater and test on rig
Stops at end of cycle a) fuel fault Ensure fuel supply to heater - fuel valve unrestricted. Check battery voltage at 20v minimum (with lights off). Lightly tap solenoid to assist if voltage is low
  b) flame detection thermo or thermistor on electronic type o/ circuit Replace thermostat, remove heater if fitted with electronic type and test on rig
  c) glow plug carbonised or o/ circuit Check battery voltage with lights off. Replace glow plug, check resistance box for heat indicating circuit complete
Stops after a few minutes a) poor combustion Check battery voltage with lights off. Ensure motor speed correct and not fouled mechanically
  b) fuel restriction Ensure fuel lines clear and filter satisfactory. Check for water content or dirt
  c) excess heat thermostat or thermistor on electronic type operating Check saloon air intake filter for restricted air flow, noted by overheat indication on outer case around output end of heater
Will not stop (cold air) a) flame detaction thermostat or thermistor (electronic type) sticking or o/ circuit Change thermostat - change heater and test on rig
  b) relay contacts shorted on auto type Replace auto panel
Running slow a) battery voltage low Switch lights off and check battery charge
  b) motor commutator or brushes faulty Tap heater lightly at fan end to check - renew heater
Excessive smoke a) battery volts low Charge battery
  b) Fuel lines drawing air Check all fuel line nuts
  c) Heater flooded with fuel Clear drain plug
Smoke entering compartments a) Smoke drawn into air intake Check excessive smoke cause
  b) Fuel pipe washer to pump defective Replace heater
  c) Heat exchange holed Replace heater

This second guide gets a little more involved and requires a good wiring diagram to identify the relays. There are two parts to it:
A) Heater does not fire
B) Heater fired but does not operate correctly

A 1 If the motor does not run, switch the heater control to vent. If the motor still does not run check the "motor fuse", check that MR relay energises and that the MR1 interlocks have closed correctly. Check that the OHR/T relay has energised and that its interlocks are closed. Check the positive and negative supply to the control panel. Finally remove the heater and examine the brushes. Renew the heater if unable to find or rectify fault.
  2 If the motor turns only in "vent" check that the saloon thermostat is not open. Unbolt the relay panel and chack that FR relay is energised after pressing the start button. Check that SR energises after FR picks up and that the glow plug switches on. If the glow plug switches on but the motor does not run after 40 - 60 seconds change the control panel.
  3 If the motor runs after the glow plug has been on for 40 - 60 seconds but combustion does not take place and the heater fails after a complete cycle (3 mins 45 seconds) check the glow plug and change if necessary. Check that the glow plug resistance is set at 4 volts and that the element gives a good glow.

Examine the combustion chamber with the glow plug removed and check that:
a) the flame ring is pushed back (towards the motor) clear of the glow plug hole.
b) the fuel slinger is in a position, complete and that it revolves with the motor.

Switch the motor to "vent" and energise the FVR relay (manually). Check that fuel is thrown into the glow plug aperture. If no fuel is seen, check the fuel tank level and the heater fuel valve. Finally check alignment of fuel slinger and glow plug hole. If unbable to find or rectify faults, change the heater.
  4 If the start button is operated but the failure light does not extinguish check that the OHR/T has energised. Check, examine and clean the plug pins on the heater jumper. If the OHR still does not energise, change the heater.
B 1 If the heater fires, but switches off when the FDR/T relay operates, check the saloon thermostat has not operated. Check that the FVR relay had energised when the motor starts to run and remains energised when the FDR operates.
  2 If the heater has a glow plug cycle (40 - 60 seconds) but the motor only runs for a short period (10 - 15 seconds) before commencing another glow plug cycle, switch the heater to "vent". Run the heater in "vent" for approximately one minute and then repeat heating cycle. If the heater still exhibits the same symptoms leave it cycling for five minutes. If fault persists set up flame detection circuit using a model 8 AVO. If unable to rectify fault change the heater.
  3 If the heater fires but switches off after a full heater cycle (3 mins 45 secs) check wether the flame detection relay hasd picked up. If it did not operate recycle the heater and check the hot air is being pumped into the saloon. If hot air is blown into the saloon but the FDR/T does not operate change the heater.
  4 If the heater fires, the FDR/T operates, but the heater subsequently shuts down with a failure light showing on the control panel, check whether the OHR/T has de-energised. If the OHR/T has de-energised, remove and clean the heater filter. If a clean filter is not available fit a blanking plate. Rerun the heater and ensure that it does not shut down through the overheat relay. If the fault persists change heater.
  5 After shutting down the heater it hould not take longer than six minutes to switch off. If the heater continues to blow cold air set up flame detection circuit using a model 8 AVO. If fault persists change heater.