Intermittent Boiler after draining radiators

[krash]

Boiler Name: Potterton Netaheat Electronic 10/16

I spent most of the day Sunday draining the radiators and then added some Fornex Central Heating restorer when refilling the header tank. Plan is to leave that for a few days and then drain again to get rid of any sludge.

Anyhow, after refilling and bleeding the radiators, I turned on the Central Heating via the programmer (set to 24 Hrs) and the Boiler fired up instantly. After roughly 3 to 4 hours, noticed that the radiators were now cold and the Boiler was not coming on at all. Checked thermostat and programmer - both on. No heating during the night, nor in the morning when I got up and left for work.

Next day, my wife popped out in the morning and when she came back the Boiler was functioning and the radiators were red hot! Then the Boiler switched off again and came on 2 hours later.

I don't underrstand why the Boiler doesn't stay operational when the programmer is set to 24 hrs (ie. Always on) - as it did before the draining and is there something I can do about it ?

 

[ArtfulBodger]

Is that a gravity HW and pumped CH Netaheat or is it fully pumped?

 

[krash]

Yes, gravity HW and pumped (Grundfos) CH.

Since posting, CH has switched itself off again after running for about 4 hours. Also vented air from pump and air bleed screw on a vertical pipe in the airing cupboard.

At a loss as to what to try next.

 

[ArtfulBodger]

Is the hot water OK when the boiler is running? any strange noises. Do you access to a multimeter?

 

[krash]

Yes - water ok. No strange noises. No don't have a multimeter.

Any advice?

 

[ArtfulBodger]

With a Netaheat get someone in. Case probably needs to be taken off, do a google search on this boiler and you'll see what I mean.

 

[krash]

I don't particularly want to get someone in now, as this weekend I'll be draining and refilling the system again. Perhaps if it persists, I'll get a plumber/heating engineer in - bit would much prefer to try out "non-technical" possible fixes first.