Central Heating Boiler problem

[Paul]

Today I have a problem with my central heating, the boiler is a Baxi Duo-tec Combi 33 HE. I have hot water but no central heating, the boiler starts to work and then switches itself off after about 30 secs. Initially I believed this was a problem with the pressure as when the boiler started the pressure dropped below the green marked area on the gauge and the boiler stopped (although I did not get an error indication E119 for low pressure). I have repressurised the system and it now shows 1.5bar but the boiler still starts for approx 30 secs then stops. I have also bled the radiators to ensure there is no air in the system.

Any help greatly appreciated Paul

[Mike P the 1st]

On Thu, 01 Apr 2010 13:27:26 +0100, Paul gently dipped his quill in the best Quink that money could buy:

I have just had all those symptons on my Baxi. Often intermittent. It would run for a week and then srart switching off as you say. Fortunatly I have a British Gas Care plan. They just about changed every sensor and finally after 8 visits, they changed the control box last week. So far so good.

Mike P the 1st

[SS]

"Mike P the 1st" wrote in message news: [e-mail]...

Also check the conensate drain pipe is clear and no build up of water in it.

[Roger Mills]

If that was blocked, wouldn't it also stop the HW working - not just the CH?

[Paul]

I have checked the condensate pipe it seems to be ok. I rang one of the ebay shops selling the PCB (which I assume is what was changed for Mike above) and they mentioned it could be air in the system. There is a vent next to the flue at the top of the boiler but this appears to be ok it's an auto vent same as the one on the pump.

If it is air in the boiler does anyone know how to get rid of it ?

Thanks for the suggestions so far.

[newshound]

To take the last point first, my Halstead has an automatic air release valve.

I've had similar symptoms in the past where the problem turned out to be a bad connection to the CH thermistor. Obviously, the controller turns off the gas on low resistance (corresponding to water hot enough), but I *assume* it also checks for high resistance / open circuit in case of a thermistor fault.

Fix in that case was to unplug and refit the connector a few times (cleaning off oxide on the pins / contacts). If you don't have the full manual you can probably download it somewhere from the web. If you follow the plumbing you may be able to tell which thermistor is which, or you could try fiddling with them both. They look from the outside a bit like car oil pressure or temperature sensors and usually have a (removable) two wire plug attached.

[Paul]

Thanks for all the suggestions, it is now fixed. It turned out I had 2 years warranty with Baxi so I called out the engineer and the problem was the wireless remote receiver on the boiler.

Paul

[david.cawkwell]

Air pressure sensor. Common fault on modern boilers.

[geoff]

Really?

How does it sense the demand for hot water

Actually its less of a problem on modern boilers that don't have mains on the APS microswitch

I don't know the duo-tech combi but, first thing to check is whether the boiler keeps sparking after ignition until it times out - this would point to a flame sensing problem

Next "30 second" probability is associated with the heat exchanger - heat is getting in but not being carried away by the water (blockage, pump failure or something) - how long does it take to recover ?

if neither of those, then the next most probable culprit is the pcb

finally (but I would dismiss this as its unlikely to have a 30 second timescale) would be the diverter valve