DIY Doctor

Boiler Heating Not Working

Postby carrspaints » Mon Feb 21, 2011 5:32 pm

[b]Hoping for some advice. I have a gas fired central heating system that is operated by a Potterton EP2002 programmer. The valve for how water or central heating is a Honeywell V4073A 3-port mid position valve.

The problem I have is that the boiler won't fire up. I have switched on both the central heating & hot water, the red LEDs on the Potterton programmer are orrange which is how it should be. The pilot light is working but the system is not getting the gas to fire up and heat the water.

I thought perhaps our recir pump had gone but I have tested that and it works fine. There is power to the Potterton controller, the room thermostat is set to high, the pump definitely works when connected to 230volts.

So I'm guessing that either the Potterton controller is faulty, or the Honeywell V4073A valve is faulty.

My question is this, can a faulty Honeyweel valve cause the system not to call for gas, or heating? I would have thought that even with a faulty valve, the recirc pump would stiill switch on, or that the gas would ignite to boil the water, even if only briefly?

Can anyone suggest what might me the issue? Many thanks[/b]. [b][/b]
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Postby Kenj » Tue Feb 22, 2011 2:46 pm

The motorised valve has switch contacts which operate to close/open a set of contacts. This sends a signal to the control pcb to start the pump.

The motorised valve may be stuck, but you can manually operate the valve by hand. With the heating and thermoststs switched on, manually move the metal lever on top of the switch and latch it behind the metal lug. You may hear the motor cycle when you do this.

Hopefully the pump and the boiler will start when you do this. If the motorised valve is faulty you can replace the head / motor only, so avoiding a drain down.

Honeywell 40003916-003 Replacement Powerhead for V4073A
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Postby uk_ducati » Wed Feb 23, 2011 7:31 pm


You should check if you are getting a switch live to the boiler first. If you are then it's the boiler at fault and not the valve

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