No hot water/heating and hot water gushing from overflow

[LindaN]

I have a Camray 5 oil boiler that had no power to it. I had a plumber out for 3 hours and decided that it was "probably" the programmer and it would be cheaper for me to replace this myself. I did replace it .. ( Honeywell ST9400C 2 channel) and yes there is power getting to the boiler but when it was fired unfortunatley after approx 5 min the boiler stopped and there was a knocking in the loft space and boiling water was gushing out of the overflow. The boiler refused to start although there was power getting to it and I had to wait several hours and then it would allow me to reset it before it would re-start and the same thing happened again. I also changed the 3 way mid position valve head but the same thing happens. I have no hot water as it goes straight out of the overflow and there is no heating either. The programmer has a wireless thermastat and I have checked that this is working.
The pump seems ok...( Grundfos Alpha2 L ) as there is power getting to it and it registers on setting PP2 I can hear water running through the water cylinder but no hot water.
Can anyone give me any suggestions as I am pulling my hair out !!!

 

[Nige F]

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The pump seems ok...( Grundfos Alpha2 L ) as there is power getting to it and it registers on setting PP2 I can hear water running through the water cylinder but no hot water.
an anyone give me any suggestions as I am pulling my hair out !!!

The symptoms point to no pump circulation (or maybe a big airlock ) I would investigate the pump first

 

[LindaN]

I wondered about both but not sure how to check if it is the pump...short of changing it...or draining the system completely then refilling to check the air lock theory. Have you any suggestions as to how to check if it is the pump without changing it

 

[regsmyth]

You should be able to hear or feel if the pump is working when you turn the heating/hot water on.
You can also loosen the big central screw - this will let any air out.
If there's an airlock the pump won't be able to move the water. It will get warm but the pipes in and out will be cold. The boiler will fire, but because the water's not moving, the water/boiler will overheat and cut out the boiler.

If there's an airlock you should try to work out where it could be in the pipework and figure out how to push the air out so the water can flow again.

But I'm sure there could be other possibilities, such as a wiring error somewhere. However, you should be able to establish if the basic system is functioning properly.

 

[ALCPlumbing]

Open the big screw head on the front with a large flat screwdriver. Pop a towel underneath it while you do it. With pump running you should see it spinning. If not use the screwdriver to try to free it.

 

[LindaN]

I've checked the pump and it seems fine and I think it is an air lock in the system as when I open the hot and then cold taps the water it the hot stops and splutters. I have then closed all the taps but the kitchen hot tap which runs but constant spluttering. I have also tried to blow back the water up the tap which has helped to increase the flow but still fierce spluttering.
Has anyone any thoughts as I am at a loss..
Oh..the automatic vent near the water cylinder has been checked for air and nothing comes out. Lots of air coming out of taps but can't seem to shift it.
I don't think there is much if any water in the cylinder but I can hear water "glugging" when I have opened the hot water taps

Drained down the whole system and refilled..opened all radiator valves and bled them also opened 3 way valve to manual. Radiators have been purged of air and water coming out as should be. Water coming out of taps ok...although there was a lot of air came from bathroom hot and cold taps.
After water had settled I fired the boiler and it seemed to be ciculating the water for a while but then boiler stopped and banging noise in the loft but no water went out of the overflow as had before...no hot water to cylinder as the pipe below not heating up. The pipework from the boiler (which is in the garage) is getting hot but it doesn't seem to be travelling far enough up the pipework to heat anything before it cuts off Can anyone help as I am pulling my hair out and at this rate I will be bald by the end of the week.
Oh ..nearly forgot. There's a drain off pipe next to cylinder and 3 way valve which I opened and it released a fair bit of air and then ran consistent and clear so I tightened it. When the pump was on I could hear water moving around the pump and 3 way valve area. Could there be a problem with pressure??? Anything...???