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Service mode › Keston

Keston boiler service mode

How to put a Keston boiler into service mode, so it holds maximum or minimum rate while you take combustion readings. 12 models from 10 Keston installation and servicing manuals, each step with the page it came from.

Grouped by manual: one manual usually covers a range of outputs. The CO₂ figures are the manual's own. Set and check them with a calibrated analyser, never by eye.

C45, C40P, C55 & C55P

Covers: C55

GC 41-930-09, 41-930-10, 41-930-25

Forcing Maximum Fan Rate

  1. Press the Mode button repeatedly until the display shows Stby.
  2. Press and hold the Mode and + key together for 2 seconds.
  3. The display will show H nn. The unit is now locked on max fan speed.

From manual WD536, page 30.

Forcing Minimum Fan Rate

  1. Press the Mode button repeatedly until the display shows Stby.
  2. Press and hold the Mode and - keys together for 2 seconds.
  3. The display will show L nn. The unit is now locked on min fan speed.

From manual WD536, page 30.

Exiting Service Mode

  1. Press the Mode button repeatedly until the display shows Stby.
  2. Press and hold the + and - keys together for 2 seconds.

From manual WD536, page 31.

GasCO₂ max rateCO₂ min rateCO max
Natural gas8.7%8.0%150 ppm
LPG10.5%9.3%150 ppm

CO₂ and CO from manual WD536, page 29. Check against the data badge.

The gas setting is factory adjusted to within the required range and should not need adjustment. (page 27)

Combi C30 & C35

Covers: C30 / C35

GC 47-930-08

Accessing Service Mode

  1. Press Menu
  2. Press Next until the desired service mode (Maximum DHW Rate, Maximum CH Rate, or Minimum Rate) is displayed
  3. Press Enter to activate the selected service mode
  4. Note that a CH demand has to already be present for this feature to be active

From manual 222363 A01, page 39.

GasCO₂ max rateCO₂ min rateCO max
Natural gas9.3% ± 0.78.8% ± 0.7350 ppm

CO₂ and CO from manual 222363 A01, page 8. Check against the data badge.

The gas input to the burner is regulated by the gas valve according to the air flow produced by the fan. It is NOT user-adjustable. Any interference to sealed settings on the gas valve will adversely affect operation and render our warranty void. (page 36)

Keston 30C

Covers: 30C

GC 47-930-03

Enter Installer Mode

  1. Turn the DHW temperature control knob full anti-clockwise.
  2. Turn the CH flow temperature control knob full anti-clockwise.
  3. Turn and hold the mode knob in the reset position for more than 5 secs.
  4. Turn the mode knob to the Winter or Summer position.

From manual 205531-3, page 41.

The gas input to the burner is regulated by the gas valve according to the air flow produced by the fan. It is NOT user-adjustable. Any interference to sealed settings on the gas valve will adversely affect operation and render our warranty void. (page 39)

Keston Combi C30 & C35

Covers: Combi C30

GC 47-930-07

Enter Service Mode Maximum DHW Rate

  1. Press Menu
  2. Press Next until Service Mode Maximum DHW Rate is displayed
  3. Press Enter

From manual 215348, page 39.

Enter Service Mode Maximum CH Rate

  1. Press Menu
  2. Press Next until Service Mode Maximum CH Rate is displayed
  3. Press Enter

From manual 215348, page 39.

Enter Service Mode Minimum Rate

  1. Press Menu
  2. Press Next until Service Mode Minimum Rate is displayed
  3. Press Enter

From manual 215348, page 39.

GasCO₂ max rateCO₂ min rateCO max
Natural gas9.3% ± 0.78.8% ± 0.7350 ppm

CO₂ and CO from manual 215348, page 8. Check against the data badge.

The air/gas ratio valve is factory-set and must not be adjusted DURING COMMISSIONING. Any interference to sealed settings on the gas valve will adversely affect operation and render our warranty void. (page )

Keston Combi2 C30 / C35

Covers: Combi 2, Combi2 C30

GC 47-830-09, 47-930-10

Setting Maximum and Minimum Rates

  1. Access Maximum DHW Rate and Minimum Rate through the menu option.
  2. The boiler will run at Maximum DHW Rate for 10 mins as long as there is sufficient cooling load.
  3. The boiler will run at Minimum Rate for 10 mins. If return temperature is under 40°C, fan runs for 30s at max rate before ramping down over 60s to minimum rate. If return temperature is above 40°C, fan ramps down over 60s to minimum rate.

From manual UIN 236467 A03, page 35.

GasCO₂ max rateCO₂ min rateCO max
Natural gas9.3%8.5%350 ppm

CO₂ and CO from manual UIN 236467 A03, page 6. Check against the data badge.

The air gas ratio valve is factory-set and must not be adjusted DURING COMMISSIONING. (page 68)

Keston Heat

Covers: Heat 45

GC 41-930-40

Force Boiler to Maximum Rate

  1. Access menu by pressing SELECT.
  2. Rotate 1st stat clockwise to 'Set Off/Sum/Win' menu.
  3. Press SELECT.
  4. Rotate to 'Maximum'.
  5. Press ENTER to activate Maximum Rate for 5 minutes.

From manual 208964 A10, page 45.

GasCO₂ max rateCO₂ min rateCO max
Natural gas9.3%8.4%–
LPG11.0%10.2%–

CO₂ and CO from manual 208964 A10, page 6. Check against the data badge.

System S30

Covers: System S30

GC 41-930-45

Accessing Installer Mode

  1. Press function button and RESTART button together for > 5s.
  2. 1: Last 3 faults shown.
  3. 2: SL shown (Min rate press RESTART).
  4. 3: SH shown (Max rate press RESTART).
  5. 4: VF shown (Venting function).
  6. Press function button to cycle through parameters (dU, P1, P7, FL, SE) and exit.
  7. To exit Max/Min rate mode: Press RESTART.

From manual 215352 A09, page 37.

GasCO₂ max rateCO₂ min rateCO max
Natural gas9.3% ± 0.78.8% ± 0.7350 ppm

CO₂ and CO from manual 215352 A09, page 8. Check against the data badge.

The combustion for this appliance has been checked, adjusted and preset at the factory for operation on the gas type defined on the appliance data plate. DO NOT adjust the air/gas ratio valve. (page 34)

The Keston 130 Condensing Boiler

Covers: Keston 130

GC 41-930-05

Initial Firing / Service Start

  1. Purge the gas supply in accordance with BS 6891.
  2. Vent the water system, ensuring water flow is established through the heat exchanger and no air pockets remain.
  3. Turn the gas service cock to ON.
  4. Turn on the electrical supply, setting any external controls to call for heat.
  5. Set the boiler On/Off switch to 'ON'.

From manual WD52/0/1997, page 21.

GasCO₂ max rateCO₂ min rateCO max
Natural gas8.9%8.2%–

CO₂ and CO from manual WD52/0/1997, page 26. Check against the data badge.

The gas setting is factory adjusted to within the required range and should not normally need re-adjustment unless the unit has also been converted to LPG as part of the installation. (page 22)

The Keston C36 Combi & C36P Combi Boilers

Covers: C36, C36p

GC 47-930-01, 47-930-02

Enter Service Mode (For Combustion Testing)

  1. Set any controls to call for heat.
  2. Press and hold the “Summer” button until the display changes to “t99” then release the “Summer” button.
  3. Measure the CO2 reading and adjust gas valve ratio screw (pos 6) as required.
  4. Use “-” button to adjust display to “t27” for low rate testing.
  5. Use “+” button to adjust display back to “t99” for high rate testing.

From manual WD388/0/2004, page 28.

ModelGasCO₂ max rateCO₂ min rateCO max
C36LPG10.6%10.4%–
C36pNatural gas9.4%9.2%–
C36pLPG10.6%10.4%–

CO₂ and CO from manual WD388/0/2004, page 28. Check against the data badge.

The gas pressure setting is factory adjusted to within the required range and does not need readjustment. (page 26)

The Keston Celsius 25 & 25P

Covers: Celsius 25

GC 41-930-06

Service Setting - High/Low Combustion Procedure

  1. Electrically isolate boiler; remove casing.
  2. Locate red bridging jumper on right-hand board (approx 18mm in, 12mm up).
  3. Remove jumper to lock rate.
  4. Restore power.
  5. Toggle user control knob On/Off: 3rd LED = High Fire; 2nd LED = Low Fire.
  6. Measure CO2 at flue test point (High: 8.5-9% NG / 9.5-10% LPG; Low: 8-8.5% NG / 8.9-9.3% LPG).
  7. Use valve adjustment screw for High fire only. DO NOT adjust Low fire screw.
  8. Replace jumper to return to normal modulation.

From manual WD209/1/2000, page 53.

GasCO₂ max rateCO₂ min rateCO max
LPG10.0%9.5%150 ppm

CO₂ and CO from manual WD209/1/2000, page 24. Check against the data badge.

The gas setting is factory adjusted to within the required range and should not need adjustment. (page 20)

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Common questions

Is service mode the same as chimney sweep mode?

Yes, in practice. Makers use different names for the same function: service mode, chimney sweep mode, test mode, calibration mode, check programme. Each one holds the burner at a fixed rate, usually maximum then minimum, so you can take a stable combustion reading.

Can I adjust the gas valve while it's in service mode?

Only where the manual gives an adjustment procedure, and only with an analyser in the flue. Many current boilers are set at the factory and the manual says not to touch the gas valve. Where a manual says that, it is shown with the procedure above.

Other makers

AlphaAristonAtagBaxiBiasiChaffoteauxFerroliGlow-wormHalsteadHeatlineIdealIntergasJohnson StarleyMainPottertonRemehaSimeVaillantViessmannVokeraWorcester Bosch

Service mode and combustion checks are work for a competent, Gas Safe registered engineer. These procedures are taken from the manufacturers' manuals and inform your judgement; they don't replace it. Always work to the manual for the exact appliance, its data badge and the current standards.