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Boxer C28 - DHW working, CH not working

Postby jono200 » Thu Jan 17, 2008 1:53 pm

I turn to this forum in the hope for some help. I have trawled the internet for a solution, but no joy.

Here is the problem:
I have a Boxer C28 boiler (it is approx. 3 years old). Hot water is working fine, but I have no/limited central heating. I say no/limited because this is an intermittent problem. This boiler is very temperamental.

When the CH is not working here is what happens:
The green LED lights on the boiler control panel, meaning there is a demand for heat. The burner ignites on the boiler, as you would expect, but then goes out several seconds after the electrodes stop sparking. Then five minutes later the same thing. This behaviour will repeat over and over. However, if I leave the boiler in this condition for long enough (anywhere from a couple of hours to days), then the boiler might eventually behave itself. i.e. The burner will stay lit until the room thermostat reaches the desired temperature.

I can assure you this problem is nothing silly. i.e. timer, thermostat setting, controller setting, etc. The user controls are set correctly.

So far I have done the following:
1) Checked the system for a blockage. I have drained/flushed/refilled the system (using an additive).
2) I have bled the system, and there is no air-lock.
3) I have checked the fan and pump are running. All seem fine. In the case of the pump there is 240v on the terminal, the rotor is free, and the pump is vibrating. I can hear water running through the system.
4) I have replaced the CH sensor on the pipe from the divertor valve.

One point about item 4). If I unclip the sensor from the pipe, the burner will stay on, but the outlet pipe gets very hot.

Please can anyone advise what the problem might be? Remember, the system heats up very well on a good day - when the boiler plays ball.

Any ideas..? PCB perhaps?

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Postby htg engineer » Thu Jan 17, 2008 7:54 pm

I cannot find any instructions for the boiler your enquiring about, and i've never worked on one.

Check the hot water draw off when the boiler comes on for the heating, is this getting hot ? it could be the diverter valve is sticking.

"One point about item 4). If I unclip the sensor from the pipe, the burner will stay on, but the outlet pipe gets very hot. "

what about with the sensor connected ? does the pipe get hot or warm ?
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Postby jono200 » Sat Jan 19, 2008 1:16 am

Thanks for the reply.

I checked the hot water pipe from the diverter valve with the heating on, and this pipe is at room temperature.

When the CH sensor is connected on the pipe between the heat exchanger and diverter valve, this is when I see the behaviour described above.

I now think the CH sensor is serving its purpose; I believe that the pipe is getting too hot, and the sensor correctly shuts down the system. This always occurs at 70c on the temperature gauge.

I have noticed that if I shut off the first radiator on the flow, then this can affect the time the burner is lit (the burner might stay on for a minute or so), but this time will reduce to seconds again after a few cycles. Re-opening this radiator will then have a similar affect.

All the valves on my radiators are manual valves and are all open. Does this mean the boiler can deliver its minimum output? Do I need to consider a bypass or thermostatic valves?

I have only lived in my house for a few months, so cannot say if the heating was ever right.
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Postby roger196 » Sat Jan 19, 2008 2:21 pm

Check that the diverter valve is actually moving when the demand for CH comes on. Holding the pipes gently about ten inches either side of the valve will tell you if hot water is flowing thru. Try the same for the pump if you can get at it.
Have you checked that the isolation valves at the boiler for the CH flow and return are both open. Is the pressure up to 1.5 bar when cold (assuming a sealed system)
It would be worth getting hold of the manufacturers instructions ( use their website to get the phone number) as they usually have very good fault finding guides. If the boiler requires dismantling, it is worthwhile getting professional help.
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