Combi boiler banging

[MartinArmstrong]

My 1yo oil fired combi boiler is giving a bit of jip at the minute that is defeating me, despite considering myself a fairly practical person. It is a Warmflow boiler from Northern Ireland, so similar to Worcester Bosch models but supposedly easier to fix as everything is easier to access. The hot water works perfectly on demand. The central heating was switched off from around March until a week or two ago but when I fired it up it was banging as if there was air between the circulating pump and the top of the boiler where the heating flow pipe goes across and down the back under the floor. The whole pipe shakes. I used the pressure relief valve to drop the system pressure away down to nothing, closed all the radiators at both sides, opened the filling loop and then opened one radiator at a time allowing each to fill and bleeding them (hardly any air at all), clockwise around the system starting at the nearest radiator. After I bled each one I closed the valves again before moving to the next radiator. I opened the bleed screw on the pump and as far as I can see water came immediately so no air there. There is also a straight connector with a small bleed screw at the top of the boiler (the highest point in the system). When I open this with the pump either running or off I get nothing but water. Since I had each radiator closed I thought I'd give the system a try and it fired up no problem. After opening one radiator at a time it continued to work so I thought I'd cracked it. This morning it started banging again (the next time it was fired up). I've done this a few times and get the same result so that I'm totally flummoxed. The heating can also be running perfectly until somebody uses the shower or hot tap and turns it off, when the heating pump starts banging again. The pump works, the heating works, so I'm sure there is air but I have no idea how to get it out!

Sorry for the really wordy post but does anyone have any ideas?

Thanks

 

[SimonG]

Its still under warranty. If you are sure its the boiler then get them out.

 

[MartinArmstrong]

I live in Southwest Scotland so the boiler was fitted by a local plumber, who didn't bother sending in the details when it was commissioned (I've just found them inside the front). In any case, Warmflow only have service people in Northern Ireland and England. If it isn't immediately obvious to somebody on here I'll just give them a call and beg for info.

 

[kris]

Hi there Martin. Normally when banging occurs it's usually a circulation problem of some kind. Are u sure the pump is working and all valves are fully open. Also any valves on filters

 

[glenntaf]

2 questions.
1. You say that the boiler was fitted a year ago. Was this to new pipework and radiators or to an existing system, and if the latter was it flushed properly before installation?
2. Does the central heating pipework go up into a loft area or similar then drop back down to any radiators??