Morning all. My CB28 is refusing to fire up, on neither hot water or the CH. The pressure is set right and the lower warning light (B) amber is flashing every second or so. I've tried operating the black clip on switch to the left of the diverter valve but not a lot happens! Any advice please?
Alpha CB28
- Thread starter M3presman
- Start date
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I presume the flashing light is the low pressure light?
You will have ignored checking pressure regularly and the boiler's switch then operated to protect the boiler against your lack of attention.
Infuriatingly, you have just said the "pressure is set right".
So I don't know what the pressure is set to because I don't know what YOU think is right.
The boiler LP switches have considerable hysteresis when old and dirty and you may need to wait a lot of time for it to reset depending on what pressure YOU think is right.
I normally set most boilers to 1.5 bar.
But without knowing what you have set it to its difficult for me to advise you properly.
Setting it to 1.8 bar could cause the switch to reset faster if I have assessed your problem correctly.
Tony
You will have ignored checking pressure regularly and the boiler's switch then operated to protect the boiler against your lack of attention.
Infuriatingly, you have just said the "pressure is set right".
So I don't know what the pressure is set to because I don't know what YOU think is right.
The boiler LP switches have considerable hysteresis when old and dirty and you may need to wait a lot of time for it to reset depending on what pressure YOU think is right.
I normally set most boilers to 1.5 bar.
But without knowing what you have set it to its difficult for me to advise you properly.
Setting it to 1.8 bar could cause the switch to reset faster if I have assessed your problem correctly.
Tony
when neon B flashes every 5 seconds it just confirms that the boiler is at rest and means nothing, you dont have low system pressure or neons A and B would flash alternatively do you mean that neon B (amber) is flashing every second ? if so you have a thermistor fault
Well you presume wrong it just means that there is power to the appliance if flashing every 5 seconds and if flashing every second it is a faulty Thermistor
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OK.
Could either thermistor being faulty prevent the boiler firing up at all?
Or only the flow one?
Most boilers will still work on CH if the DHW one is failed.
Some ( better designs ) will even work on DHW but at a lower power level even if the DHW one is failed.
Could either thermistor being faulty prevent the boiler firing up at all?
Or only the flow one?
Most boilers will still work on CH if the DHW one is failed.
Some ( better designs ) will even work on DHW but at a lower power level even if the DHW one is failed.
Many thanks for taking the time to reply. The boiler pressure is set at the top side of the green shaded area on the gauge approx. 1.5bar. When the tap is open I can hear noise from the boiler which I'm assuming is the pump but it just wont fire. I've read about the diverter valve on other threads on here, but neither the HW or the CH work, so I'm not thinking its connected to that.
Yes, your pressure is OK.
Ian has identified that if its flashing once per second then one of the temperature sensors has failed. There are two and if the plug is properly attached and the pins not corroded then probably just failed open circuit.
The resistance can be measured and should probably be around 10K with boiler cold.
It is a relatively simple repair as a DIY but needs the usual skills dealing with electrical components and water content.
Or a simple repair for an engineer.
Tony
Ian has identified that if its flashing once per second then one of the temperature sensors has failed. There are two and if the plug is properly attached and the pins not corroded then probably just failed open circuit.
The resistance can be measured and should probably be around 10K with boiler cold.
It is a relatively simple repair as a DIY but needs the usual skills dealing with electrical components and water content.
Or a simple repair for an engineer.
Tony
It might be the primary temp sensor which is inside the combustion chamber. What's your advice there?
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