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Plumbing and Gas News

Practical tips for maintenance, service and repairs of plumbing and gas appliances

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Maintenance and Service


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



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



Vaillant Boiler goes to lockout after 2 hours after reset

Boiler has started to shut down with the overheat lamp lit. This happens after the boiler has been running for at least 8 hours. Once reset, it will run again for a number of hours before tripping out again. The problem is more likely the central heating system than the boiler. Basically the hot water is not getting out of the boiler fast enough so that when the flame goes off the residual heat in the boilers internal heat exchanger causes the water to become overheated and trip the safety device.

  • Has the pump speed been turned down? Turn it up to maximum.
  • Do you have radiators and /or towel rail that have manual valves on (not thermostatic) to accept a flow of water when other rooms with thermostatic valves on have warmed up? If so are they open?
  • Have you recently insulated some pipework that is meant to be uninsulated as part of a heat sink / by pass system.
  • Is there a lot of air in the system preventing proper circulation?
  • Is the system working properly otherwise? sludge in the system may prevent proper circulation.
  • Is the flue is not blocked?
  • Does the pump connected to overrun?
  • Is by-pass valve opened?



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



Ariston Microgenus HE Combi Boiler - Fault A01 faulty PCB replacement 65103422 (Replaces 65102571)

Ariston Microgenus HE Combi Boiler  works for 7 seconds and then goes to a lock-out with a fault code A01 on a screen

  • Turn the central heating or hot water on
  • remove the front cover and watch the spark electrodes
  • If they continue to spark after the flame is present then check the flame sensing electrode (the left hand side one)
  • if it looks intact then check the wire from it to PCB for continuity with a multimeter
  • If there is a continuity then  replace a PCB
  • The replacement part number is ARISTON PCB (PRINTED CIRCUIT BOARD) 65103422 (REPLACES 65102571) (MICROGENUS HE 24,28 & 32)


PDF - Ariston Microgenus HE Combi Boiler - Fault A01 faulty PCB replacement 65103422 (Replaces 65102571) - installation instructions


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