Switch to mobile site

Maintenance and Service

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

Create an Article



Click to show/hide index







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



Main Combi 24 HE - Intermittent hot water. Faulty diaphragm 5111137

Main Combi 24HE boiler is constantly leaking from the bottom

  • Hot water does't always come on. It seems like the boiler is temperamental and decides by himself whether to heat the water or not. 
  • The leak doesn't affect the system pressure
  • Check the nut and the diaphragm inside the flow-switch valve. If the diaphragm has holes in it then replace the diaphragm
  • The part number is 5111137
  • To replace isolate the water supply to the boiler.
  • No need to drain the central heating
< Go Back2016-04-29

Main Mersey Super multipoint water heater - faulty automatic valve 2106378

Main Mersey Super multipoint water heater makes a very loud scary noise

  • Flame doesn't go off after hat water tap closed
  • Steam coming from a hot water tap and loud noise from the water heater
  • The Automatic valves pin has got stuck
  • Remove the bottom cover from the water governor at the back of the boiler
  • Find a metal pin sticking out and try to move it up and down
  • If it moves then lubricate it and reassemble the water governor
  • If the pin has got stuck permanently then replace the Automatic valve 
  • The part number is: Main 2106378 automatic valve assembly
< Go Back2015-08-01

Main Combi 24 HE - Radiators are getting hot when hot water tap is opened. Faulty Hydraulic Venturi 24805

Main Combi 24 HE - Radiators are getting hot when hot water tap is opened.

  • Open the boiler casing and find the water flow switch at the front, left, bottom side
  • Open the hot water tap and check if a spindle is moving forward to activate a micro-switch
  • If the spindle is not moving at all then replace the diaphragm inside the flow switch valve. You will need to isolate a cold water supply to the boiler
  • If the spindle is moving slightly but not far enough then look at the venturi which is located inside the hydraulic unit on the right hand side of the boiler
  • To replace the venturi you will need to isolate the cold water supply to the boiler
  • the part number is Hydraulic Venturi 248051 or 248050 
< Go Back2015-07-06

Main Combi 24 HE - Hot water is lukewarm faulty water pressure switch 248063

Main Combi 24 HE - Hot water is lukewarm. Faulty water pressure switch 248063 

  • The radiators are getting hot when hot water tap is opened
  • Open a boiler casing and check the pressure differential valve spindle
  • If the spindle is not moving or not switching the micro-switch when hot tap is opened then replace the BAXI PRESSURE DIFFERENTIAL ASSEMBLY 248063
< Go Back2015-05-23

Main Main Combi 25 Eco Elite - makes a loud noise when igniting or goes to a lockout Baxi Ingition/Ionisa

Main Combi 25 Eco Elite - makes a loud noise when igniting or goes to a lockout 

  • The flame sensing electrode has bend and dislocated 
  • It allows more gas enter the combustion chamber before ignition occurs
  • this causes the banging noise
  • Replace the ignition assembly
  • The replacement part is Baxi Ingition/Ionisation Kit 5130293
< Go Back2015-05-21

Main Combi 24 HE - boiler often goes to an ignition lockout

Main Combi 24 HE - boiler sometimes goes to an ignition lockout

  • Open an electric board cover and when boiler is in the lockout state make a circuit between blue and purple wire coming from the air pressure switch
  • If boiler starts working then replace the air pressure switch
  • The part number is 5137532
< Go Back2013-10-18

Main Combi 24 HE - Hot water is lukewarm

if I don't turn on the hot tap quite so fully, I got a much hotter water coming out of the bath tap. The kitchen sink always seemed to produce very hot water while the bath tap didn't. I've concluded that the reason is that the kitchen tap has a narrower spout and therefore a slower rate of flow than the bath tap. If the bath tap is turned full on, the combi therefore can't heat up the water fast enough.

  1. Diverter valve is faulty.
    1. Turn your central heating off and allow to cool for 45 minutes, important the CH must be cool.
    2. turn your domestic hot water on only at the kitchen tap, run till hot, decrease slightly, get water as hot as you can, allow to run for 5 minutes.
    3. With tap run running locate flow and return CH pipes under combi' they should be cool to the touch,
    4. if not the diverter valve have to be replaced.
    5. The replacement part is BAXI 248062 VALVE 3 WAY ASSY
  2. Scaled up plate heat exchanger. Well you can put general cleaner in the system, which will pump through the heat exchanger, and should remove scale albeit slowly. You then have to drain and flush the system a few times. Or you can drain down the boiler and remove the heat exchanger and put some directly in to it and leave it to descale (with DS30 or similar). Alternatively, you can hire a machine to pump descaler chemical back and forth through it, or take it to a local plumbing shop which offers the same service. Or if its really badly scaled and old, and you can get one cheap, and you value your time just replace it with a new one.

Boiler manual PDF

< Go Back2013-02-02

Main Combi 24 HE - Flame failure light on boiler

Combi boiler Main 24 HE was fitted about four months ago and it's been fine up until today when the flame failure light flashes when you turn the hot water tap on. I've had a look at the troubleshooting section in the boiler manual and have tried resetting to no avail. I have also checked the pressure gauge which seems fine. The book says that the boiler may have over heated, it has been on non stop since last night so I've left it to cool, but failing that, any ideas what the problem could be?

  1. condensation trap blocked, clear it
  2. minimum burner pressure should be checked,
  3. on/off/reset switch to be checked/replaced,
  4. check Electrode and flame sensing lead,
  5. air pressure switch, ( unlikely ),
  6. then and only then should you suspect the PCB.

Boiler manual PDF

< Go Back2013-01-28

Main System HE - Flame goes off after 10 seconds.

The PCB is faulty (5112380) or flame sensing electrode is not positioned correctly or broken. If there is 1µA current on a sensing electrode, then PCB need replacement. Otherwise the sensing electrode. Main technical support number is 0844 871 1570. The gas valve is faulty if when boiler is in the lock out there are 20 VDC across two black wires for the main solenoid valve.

Boiler manual PDF.

< Go Back2013-01-23