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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



Potterton Prima F - faulty PCB 407677

Potterton Prima F - faulty PCB 407677 - the boiler does not ignite.
The fan is running and the air pressure switch is clicking however there is no spark or ignition.
Check that there is 240V between T2 and T4 on electronic board while fan is running.
If there is then replace the PCB. The part number is 407677

< Go Back2019-06-09

Potterton Prforma 24 - intermittent clicking and hot water

Potterton Prforma 24 - intermittent clicking and hot water

Remove the cable from the gas valve and check resistance.
​Between top 2 pins and bottom 2 pins on the gas valve resistance should be around 2 kOhms. Between top and bottom pin resistance should be around 5kOhms. If no resistance then replace the gas valve.

< Go Back2019-06-02

Potterton Performa 30HE - faulty PCB 5112380

Potterton Performa 30HE - no heating no hot water.

  • The boiler doesn't react on controls
  • Pump doesn't run and no power to the pump
  • faulty PCB 5112380  
< Go Back2018-01-28

Potterton Suprima 80 HE - Faulty PCB (SM10501U)

Potterton Suprima 80 HE - pump overun doesn't work

  • Boiler occasionally goes to an overheat lockout
  • The pump is wired to a PCB pump connection to provide 2 minutes pump override in order to get rid of the het from the main heat exchanger.
  • The faulty part is PCB - part number is SM10501U
< Go Back2017-09-17

Potterton Profile - faulty thermostat 907729

If boiler intermittently cutting off and requires to press a reset button then replace the themostat

Part number is 907729

< Go Back2016-03-25

Potterton Suprima - Faulty fan 40958801

Potterton Suprima boiler does not ignite and goes into a lock out after 10 seconds

Replace the fan

The part number is 40958801

< Go Back2016-03-25

Potterton Housewarmer 45 - Faulty PCB replacement (407725)

Potterton Housewarmer 45 back boiler does not ignite

  • Put a temperature control on maximum on a user control. If there is no green light on check sparking
  • If there is no sparking occurs and gas valve is not opening then check DC voltage from user control unit to PCB between ports 8 and 9 (pink and black)
  • The DC voltage should be between 1.5V and 3V
  • If the voltage is out of range then replace the User control
  • The replacement part is Potterton Houseware 45 / 55 Boiler - User Control Assy 407726
  • If the problem remains after the User control replacement then replace PCB
  • The replacement part number is BBU flame monitor & ignition control PCB 407725
  • Note that both of the parts are obsolete and not produced by the manufacturer any more
< Go Back2015-03-13

Potterton Performa 24 - faulty thermistor (NTC temperature sensor 5108265)

Potterton Performa 24 combi boiler doesn't have any heating or hot water

  • There are no ignition lock-out lights on the front panel
  • The pump is constantly running
  • Boiler attempts to ignite every so often
  • Flame goes off once the spark stops
  • Gas inlet pressure should be 20 mbar
  • Maximum burner pressure should be 12.2 mbar
  • Resistance on a gas valve solenoids should be:
    • Top 2 pins - 1.3-1.5 kOhm
    • Bottom 2 pins - 2.8-3.1 kOhm
  • Resistance on a thermistor:
    • at a room temperature - 14kOhm
    • at 80ºC - 2kOhm
  • If the thermistor's resistance is around 34kOhm at higher temperatures then replace the thermistor
  • The replacement part number is Baxi Potterton 5108265 screw in type Temperature Sensor
    • Old part numbers: :248068, 247394
    • No need to drain the boiler - its in a dry pocket

PDF - Potterton Performa 24 - faulty thermistor (NTC temperature sensor 5108265) - installation instructions

< Go Back2014-12-23

Potterton Suprima 60 - faulty PCB 5111603 (replaces 408850)

POTTERTON SUPRIMA 60 boiler doesn't fire up and the green light on a control board rapidly flushes



< Go Back2014-12-20

Potterton Promax Combi 28 HE A - Faulty diverter valve and motor

Potterton Promax Combi 28 HE A blows the internal 2 amp fuse after a couple of minutes of work

  • Check the diverter valve for leaks
  • Remove the diverter valve motor and check if its wet
  • If it is wet then replace both the diverter valve and the motor
  • Be careful there are 2 types of diverter valves for this boiler
  • One with the internal bypass with a pipe going to the pump (you can get a replacement cartridge for it)
  • The second one is without bypass and you need to replace the whole valve
  • The motor is the same for both
< Go Back2014-12-19

Potterton Puma 80e - faulty diverter valve replacement (8929899)

Potterton Puma 80e combi boiler doesn't have any heating but hot water is working fine

  • turn the heating on and check the flow and return pipes
  • if the flow pipe is getting hot but return pipe remains cold than it can indicate a faulty diverter valve, pump or blockage in the main heat exchanger
  • if the boiler is firing up but goes into a low flame almost straight away and then flame goes off without overheat lock-out then diverter valve is faulty and needs replacement
  • the replacement part number is Potterton Puma 80 Diverter Valve 8929899 10/20351

PDF - Potterton Puma 80e - faulty diverter valve replacement (8929899) - installation instructions

< Go Back2014-12-14

Potterton Suprima 40,70 - faulty gas valve 402550 (VK4105E 1007)

Potterton Suprima 40,70 - Pump is running, fan is running and ignition occurs but no flame

  • Connect a U-gauge to p2 point on a gas valve, reset boiler and heating and hot water demand
  • If there is no pressure on the gas valve outlet then turn the electricity off
  • Remove the electrical connector from the gas valve 
  • Check DC voltage between blue and brown should be 210V DC
  • If there is a voltage coming in to the gas valve then replace the gas valve
  • The replacement part is: Potterton Suprima 30-80 gas valve 402550 (VK4105E 1007)
< Go Back2014-11-30

Potterton Profile 100e - faulty PCB 407677

Potterton Profile 100e boiler doesn't fire up

  • The fan is running
  • The air pressure switch is OK
  • Spark occurs
  • No gas is coming out
  • Check the gas supply is present
  • Check the 240 Volts between T2 and T3 on electrical control board. If No then replace PCB
  • Replace the Control Board. Part number is Potterton 407677 P.C.B. Boiler Control, fitted with 1A Fuse
    • Disconnect six way plug, two way plug and electrode lead
      from the electronic control.
    • Disconnect the flying leads of the electronic control as follows:
      • white wires from the control thermostat
      • brown wire from overheat thermostat
      • blue wire from boiler terminal block connection N
      • green/yellow wire from earth post
    • Release the control by lifting it from the four retaining lugs.
    • Remove electronic control.
    • Replacement is the reverse of removal. NOTE: Polarity of
      electrical connections on thermostat is not important.
    • Follow the full commissioning procedure as detailed in the
      COMMISSIONING section of manufacturer's instructions. Page 18.
< Go Back2014-11-10

Potterton Netaheat 10/16 Electronic - Air pressure switch replacement 642204

Potterton netaheat 10/16 Electronic doesn't fire up.

< Go Back2014-05-31

Potterton Performa 30 HE - DHW diaphragm replacement

Potterton Performa 30 HE - Heating is working but no hot water

  • Open a hot water and check if a pin on a diverter valve is switching a micro-switch
  • If it does then replace a micro-switch
  • If the pin is not moving then replace a diaphragm inside
  • The part number is: Baxi 5111140 DIAPHRAGM REP KIT DHW
< Go Back2014-04-18

Potterton Performa 24 Eco HE - Air pressure switch 5137532

Potterton Performa 24 Eco HE - hot water temperature fluctuates between hot and worm.

  • The boiler flame goes off instead of a 'reduced flame mode' when water temperature is reached
  • Check the gas valve by pulling out one of the black wires and see if the boiler goes into the smaller flame mode
  • In my case an Air pressure switch was faulty
  • The replacement part number is Main Pressure Switch 5137532 (Replaces Part Number: 5112999)
< Go Back2014-02-15

Potterton Combi 80 - Overheat lockout after closing a hot water tap

Potterton Combi 80 goes to overheat lockout after opening and closing a hot water tap

  • Potterton Combi 100 DHW Diaphragm Flow Switch 10/18676 is faulty 

  • Potterton Microswitch 21/18677 to be replaced together

< Go Back2014-01-02

Potterton Profile 100e - faulty fan 409569

Boiler Potterton Profile 100e doesn't fire up, pump is running.

  • Open the boiler casee and check voltage to the fan. If 2 red wires have 240V but the fun doesn't run the n fan is faulty aneed replacement
  • The replacement part is 409573 or 409569 Baxi Fan Assembly GC Number 382445
< Go Back2013-12-26

Potterton Combi 80 - Loosing a lot of pressure

Potterton Combi 80 - Loosing a lot of pressure. Need to top up water every day.

  • Check the pressure discharge pipe outside the building if its leaking water constantly
  • Replace the pressure reliese valve PRV if it is
  • Before replacing PRV inflate the expansion vessel up to 1.5 bar
  • The part number for replacement: Potterton Pressure Relief Valve 5000721
< Go Back2013-11-29

Potterton Puma 80e doesn't have any lights on a control board

Potterton Puma 80e doesn't have any lights on a control board, no heating or hot water

  • If the boiler doesn't show any live then check
  1. an electrical supply to the boiler
  2. 2 amp fuse on the main control board
  3. a transformer has circuit on boith coils
< Go Back2013-10-22

Potterton Suprima 40L - Ignition lockout, no spark occurring

Potterton Suprima 40L boiler doesn't ignite and goes to a lock out. Resetting the boiler doesn't help.

  • Fan is working fine
  • Air pressure switch is ok
  • Ignition electrode and harness is ok
  • If all of the above are working fine then the PCB need replacement
  • The new part number is 5111603
< Go Back2013-09-29

Potterton Performa 24 - goes to overheat lock out

Once control knob turned to a hot or heating mod the boiler ignites without demand and starts making a banging noise then goes to an overheat lockout. 

  • the hot water microswitch has stuck in 'on' position
  • the part number to be replaced is Potterton Cable 248207
< Go Back2013-06-07

Potterton Netaheat Profile 50e - faulty PCB

Netaheat Profile 50e - faulty PCB. When you turn the boiler on and the pump is running but the fan works intermittently and neither ignition happening nor spark electrode working then the relay on PCB has gone. You will need to replace the whole PCB. Do not test the boiler with an opened case. This boiler works on a positive pressure and the pressure switch will never make it until the casing is closed. Isolate an electrical supply to the boiler before replacing the PCB.

Potterton Netaheat Profile 50e PCB: The part number for replacement is 407677 and you can order it from here.

Potterton Netaheat Profile 50e manual: PDF

< Go Back2013-04-25

Potterton Netaheat Profile 50e - doesn't fire up

Profile Netaheat Profile 50e - doesn't fire up.When I turn the boiler on the fan starts to spin OK but noting else happens for quite a long time  between 10 and 20 mins, eventually the ignition will spark and the gas jets will light, "visible through small glass window".  It is likely to be the casing seals or fan proving switch. Check that the casing is fitted properly & the screws are tightened. Check if the proving switch operates shortly after the fan comes on. The proving/air pressure switch is located at the other end of the silicone rubber pipes that connect to the fan outlet. You will need a multimeter to carry out this test.

The part number is 64220802 and you can order it from here.

Profile Netaheat Profile 50e manual: PDF

< Go Back2013-04-07

Potterton Powermax HE - e.01 fault code

Potterton Powermax HE - E01 fault code and it goes to lock out. Firstly code E01 is high primary water pressure in the boiler. The usual reasons for this happening are the filling loop is passing water either not turned off fully or leaking or you have a problem with the expansion vessel. Check the filling loop first as that's the easiest and if its not that then you need to isolate the boiler from the heating system and release the pressure from the boiler using the drain off provided on the boiler. Locate the pressure vessel which is usually a large red sausage or round pillow type item and there is a car tyre type valve on it. You will need a tyre pressure gauge to check that you have around 3/4 to 1 bar pressure in this. If it has gone flat they try pumping it up to the afore mentioned pressure. You could before you release the pressure from the boiler just try taking the cap off this valve and depress the little pip in the centre and see what comes out. It should be air but if you get any sort of quantity of water then this vessel will need replacing. It can also be a pressure sensor switch if expansion vessel is OK and it needs replacement.

The part number for replacement is 5107764 and you can order it from here.

Potterton Powermax HE manual: PDF

< Go Back2013-04-07

Potterton Suprima 40L - lockout twice a day

Boiler Potterton Suprima 40L goes to lock out several times a day. The central heating system was very dirty and a powerflush has been done. The powerflush didn't help much and the boiler continued to lock out. Next we need to check a thermistor, overheat stat and PCB. The thermistor has a good readings and an overheat stat does make a circuit. The PCB has a burning marks on it. Its faulty and need replacement. The part number for PCB is 5111603. The PCB can be ordered from here.

< Go Back2013-02-20

Potterton Prima 50C - Boiler is not firing but pilot light is on

Potterton Prima  60C boiler, about 12 years old, which is repeatedly tripping the spillage detector. The separate CO detector in the house isn't picking anything up. When the button is reset the boiler runs fine and sometimes cycles off and on as it should. At other times, though, the detector trips again (presumably when the room thermostat shuts the boiler down), and there doesn't seem to be any pattern to it. It's become much more frequent over the past 2 or 3 days -- yesterday it seemed to be tripping every time the boiler shut down.

If the main burner fails to light turn the boiler thermostat to the off position and check that the spillage detector thermostat reset button is pressed in, then repeat operation.

These devices do exactly what it say on the tin. This sounds like a flue problem. As you mentioned; when open the door sometimes it can trip. This may not happen on all occasions and the weather (temperature. air pressure and wind direction) can play tricks with problem chimneys.

  • I would get the flue/chimney properly surveyed to ensure it complies with the requirements on BS5440 part 1. This includes proper testing. In addition to this ensure ventilation into the room where the boiler is located complies with BS5440 part 2 and of course manufacturer instructions.
  • One further point; is the boiler in a compartment? If so I seem to remember that this model of boiler is not suitable for compartment installations. This too can cause nuisance tripping.

Boiler manual PDF

< Go Back2013-02-02

Potterton Prima 50C - Boiler goes to lockout 2 times a day

If it locks out in the morning it may be the spark electrode that gets damp overnight if it has a hairline crack in it, it will usually recover once it has some voltage put through it, hence it lighting on the second attempt, and sometimes the gas control valve sticks. If it is overheating then I would usually check the system and bypass first, and I would replace the overheat and boiler stat sensors before shelling out for a costly pcb.

Boiler manual PDF

< Go Back2013-01-27