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Maintenance and Service

Exam revision materials for Plumbing Level 2&3 and ACS Gas Safety test

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HUB-001A-WAX Vado Thermostatic Cartridge


Hudson Reed




S960134NU Thermostatic Cartridge

Sirrus Rothwell R995 Antique Shower








Alfa Laval






Electroheat PLC





Heat Lline








Saunier Duval


Viessmann Vitodens 100 W Compact



Space Heaters




Armitage Shanks





Bathstore Thermostatic Cartridge

Servicing Guide



Thermal Store Cylinders


Underfloor Heating





Hot Water Cylinders




Gas Safety Inspection

Gas Flue Analysers

Gas Hobs



Worcester 532/i - Error C6, Faulty fan 87161160670; 87172044530; 8716118443

Worcester 532/i - No heating, no hot water, the boiler displays an error code C6 

  • Check the power to the fan between brown and purple wires. If there is 240v but fan is not working replace the fan. 
  • Faulty part is fan - replacement part 87161160670; 87172044530; 8716118443
< Go Back2017-09-17

Worcester Highflow 400 RSF - No heating. Faulty diverter valve (87161207390)

Worcester Highflow 400 RSF - No heating. Faulty diverter valve (87161207390)

  • The boiler is constantly running and goes into lock out every so often
  • The hot water is working bu no heating
  • Open the boiler cover and check the diverter valve for leaks
  • Does the diverter valve operate? NOTE: This failure would cause cold water at the flow outlet and the boiler will cycle on the heating control stat.
  • Open a PCB casing and check if there is 230V at pin 3 of terminal X7?(Brown wire)
  • If NO Replace the control board if YES Replace the diverter valve
  • The replacement part numbers: Worcester 87161424820 D/valve Now 87161207390 : Bosch
  • Driver Board Pump Over-run 87161463120
< Go Back2017-03-03

Worcester Worcester Greenstar Junior 24i, 28i - Faulty MT10 Single Channel Mechanical Boiler Clock (7716192036

Worcester Greenstar MT10 Single Channel Mechanical Boiler Clock 7716192036 is faulty

  • It can turn itself on when it's not supposed to be on.
  • The selector switch between "ON" "OFF" "TIMER" does not diffirintiate  

To replace the clock remove the boiler front casing and remove one screw from the bracket which holds the clock. With power off to the boiler repalce the part.

< Go Back2017-01-19

Worcester 24i - broken temperature control knob 87161410440

Worcester 24i combi boiler temperature control knob is broken 

Replace the knob

The part number is 87161410440

< Go Back2016-03-25

Worcester 24CDi RSF Combi - Faulty fan 8716120034

Worcester 24CDI RSF- Worcester 8716120034 Fan Assembly replacement 

  • Boiler GC number is 47 311 30
  • The hot water indicator is flushing fast red after 20 seconds of heating or hot water demand
  • Reset the boiler by pressing a red button on the front panel
  • Turn the room thermostat on or open a hot water tap
  • Open the boiler cover and check the voltage to the fan assembly
  • If there is 240V but the fan is not turning then replace the fan
  • The part to replace: WORCESTER 24CDI RSF / 24SBI FAN – 8716120034
< Go Back2016-02-06

Worcester Greenstar 30CDI Conventional boiler - F0 error - full boiler reset

Worcester Greenstar 30CDI Conventional boiler shows F0 error code and not working

  • The error code appears sometimes only
  • F0 means boiler internal error
  • PCB requires a full reset
  • Full reset procedure:
    1. Press  Spanner button for 8 seconds
    2. Press Eco and Suitcase buttons simultaneously until 8A on a display
    3. Press Eco button to 8E on a dysplay
    4. Press Ladder button for 5 seconds until display shows 00
    5. Press Ladder button once to complete the full PCB reset
  • If after a full reset error code F0 continues then replace PCB
< Go Back2015-07-24

Worcester Greenstar Ri 24 - Faulty PCB replacement 87186871640

Worcester Greenstar Ri 24 open vent boiler works intermittently

< Go Back2015-07-13

Worcester Highflow 400 ELECTRONIC - Hot water temperature flactuation

Worcestr Highflow 400 ELECTRONIC combination free-standing storage boiler has a problem with a temperature of Hot water

  • Luke-warm temperatures in all operating modes
    • Modulating valve not opening.
    • Create a DHW demand and fully open a tap. Measure the voltage across the two tags on the modulating gas valve. Is it over 10Vdc?
    • Yes - Replace gas valve.
    • No - Check wiring to control board. If o.k. replace control board. It is wise to  also replace the modulating valve in case this was the cause of board failure.
  • Low DHW outlet temperature in DHW mode:
    • Scaled / inefficient water to water heat exchanger. Replace.
    • Replacement part number is DHW Heat Exchanger - 8 716 142 904 0
    • To replace the heat exchanger you will need the left hand side panel to come off

PDF - Worcester Highflow 400 ELECTRONIC - Hot water temperature flactuation - installation instructions

< Go Back2015-04-26

Worcester Greenstar R 25HE - C1 error, faulty fan 87172043730

Worcester Greenstar R 25HE combi boiler displays C1 error. no heating or hot water

  • C1 error means a low fan speed
  • The fan or PCB is faulty
  • To check remove the power cable from the fan
  • Turn the heating or hot water on
  • Measure voltage between  blue and white
  • If there is 240V then replace the fan
  • The replacement part is Worcester 87172043730 Fan Assembly
< Go Back2014-10-18

Worcester 24CDI RSF Combi - Pump replacement 87161431080

Worcester 24CDI RSF Combi boiler shuts off after about 10 seconds when it starts making a loud kettling sound

  • Kettling sound means a poor circulation in the system
  • It could be due to a faulty pump, blocked heat exchanger or faulty thermostat
  • To test torn the central heating on and check if there is any power to the pump
  • If there is a power but the pump doesn't circulate then replace the pump
  • The replacement part is Worcester 8-716-143-108-0 Pump
< Go Back2014-10-11

Worcester 24i standard efficiency - 77161920020 cdi-mechanical timer replacement

Worcester 24i standard efficiency combi boiler timer doesn't work

PDF - Worcester 24i standard efficiency - 77161920020 cdi-mechanical timer replacement - installation instructions

< Go Back2014-05-17

Worcester 24CDI - Worcester 87161202820 Fan Assembly replacement

Worcester 24CDI - Worcester 87161202820 Fan Assembly replacement 

  • The hot water indicator is flushing fast red after 20 seconds of heating or hot water demand
  • Open the boiler cover and check the voltage to the fan assembly
  • If there is 240V then replace the fan
  • The part to replace: Worcester 87161202820 Fan Assembly replacement 
< Go Back2014-04-05

Worcester Greenstar 24i Junior - Faulty Worcester Fan Assembly 87161160670

Worcester Greenstar 24i Junior combi boiler doesn't fire up, blue light fast flush

  • Turn the heating on or open a hot water tap
  • Boiler goes into lock out after the pump starts spinning
  • Remove one of the orange wires from the overheat stat and watch the fan
  • The fan should start spinning to remove excessive heat from the burner
  • Check the voltage to the fan between Brown and Purple wires
  • If the voltage is 240V then the fan is faulty
  • Replacement part number is Worcester Fan Assembly 87161160670
< Go Back2014-03-03

Worcester 24CDi RSF Combi - Faulty diverter valve diaphragm 87161405530

Worcester 24CDi RSF Combi doesn't produce any hot water unless the heating is on

  • Open a hot water tap and check a diverter valve pin under the boiler is moving forward to turn a micro-switch on
  • if it doesn't move or touches the micro-switch then the diaphragm is faulty
  • replacement part number is Worcester Diaphragm Replacement Kit 87161405530
< Go Back2014-02-28

Worcester Greenstar 24i Junior - Leaking, no heating

Worcester Greenstar 24i Junior combination boiler is leaking from underneath and the central heating stopped working:

  • Worcester Flow sensor adaptor is leaking onto the diverter valve motor which gets damaged hense the central heating doesnt work
  • Need replace the flow sensor adaptor the part number is 87161064330
  • Need to replace Worcester Diverter Valve Motor 87161068470
< Go Back2014-01-17

Worcester 24i Junior - flashes once a second

Worcester 24i Junior - flashes once a second and no heating and hot water

  • If the pump or fun doesn't run you need to check Pressure switch
  • It's located to the right next to the heat exchanger
  • Check the continuity across two orange wires
  • If no continuity then replace the Pressure Switch
< Go Back2013-11-23

Worcester Greenstar 24i Junior - makes a very loud noise and stops working

Combi boiler Worcester Greenstar 24i Junior - makes a very loud noise after some time and goes to ignition lock out (blue indicator flushes slow: normally off, flushes on)

  • This boiler doesn't have a signal from condensation trap when its full
  • The condense pipe is blocked and when water reaches the burner it starts blowing the flame off
  • This is where the loud sound is coming from
  • Also there is a kettle like sound coming from the burner
  • Clean the condensation trap and unblock the condensation pipe to fix the problem
< Go Back2013-10-13

Worcester 28i Junior - Pump replacement

Worcester 28i Junior standard efficiency boiler goes to overheat lock out and makes kettle noise.

  • The most likely reason for this fault is a faulty pump
  • To test the pump open the casing and turn the heating on
  • If the pump does not vibrate on heating or hot water demand then check the voltage to it
  • If there are 240V to the pump on demand but it doesn't work then repalce the pump
  • The part number is 87161056560
  • Otherwise its PSB
< Go Back2013-10-12

Worcester Greenstar 24i Junior - is leaking from various places under the boiler

Worcester Greenstar 24i Junior combination boiler was leaking from various places under the boiler. In my case the hydraulic assembly had a crack and was spraying water so it seemd lek the whole boiler was leaking.

  • To replace the hydraulic assembly you will need to drain the boiler and isolate the cold water supply
  • The part number is 87161063560
  • It was a very difficult part to replace
< Go Back2013-10-07

Worcester 24i Junior - flashes 4 times per second

Worcester 24i Junior combination boiler doesn't start and goes to ignition lockout (flashes amber 4 times per second):

  • take the cover off and see if the fan is running
  • if boiler works fine with the cover off and the fan is working fine then replace the air pressure switch (ISP). The part number is 87161044610
  • if with the cover off after short time the fire from the burner starts spreading from under the burner it means the fan doesn't go to the second speed and the printed circuit board (PCB) has to be changed. The part number is 87483004840.
  • How to test the transformer: the resistance between bottom 2 pins should be 40-100 Ohms
  • How to test fan: the resistance between black and white should be 75-155 Ohms
< Go Back2013-09-20

Worcester Greenstar 30CDI Combi C6 fault code repair

Worcester Greenstar 30CDI Combi - C6 fault code appears on a display and the boiler gives no hot water or heating at all. This error code in 9 cases out of 10 means the fan problem. To make sure it is a fan but no a PCB remove the boiler casing. Isolate electrical supply to the boiler. Remove the electrical connection from the fan and connect your multimeter to a brown and purple wires. Turn the electricity back on and put the boiler on heating or hot water demand. If a multimeter shows 240 volts then you need to replace the fan otherwise check harness to the fan for continuity or PCB for burner marks.

Fan: The part number for replacement is 87172044530 and you can order it from here.

< Go Back2013-04-20

Worcester Greenstar 24i Junior - timer is not working

The boiler works fine when you put it on constantly on and if you want to turn it off but doesn't work on timer. The most likely you need to replace the mechanical timer. Turn the electricity off and remove the boilers cover. This is a very easy part to change. Unscrew one screw holding it and pull it upwards. Disconnect the wires and plug in the new one. The part number for the mechanical clock for Worcester Bosh is 7716192036 and it can be ordered from here

Boiler manual: PDF

< Go Back2013-03-03