OT - New boiler been fitted

[Andy Cap]

I had my old reliable but ageing Spacesaver replace by a Vaillant 428 about 8 weeks ago. It's a straight-swap on an open-vented system, the only changes being a replacement bypass valve, a new pump and a Magnaclean !! device.

Since day 1, first thing in the morning it sounds like a waterfall ! I have bled various radiators numerous times and last night, the one on the landing, where what little air used to collect was I guess, half empty. The one in the hall, where I never had any air from, I estimate was a 1/4 air.

There has been no leaks as far as I can tell - there is nothing below the ground floor level - so how might this huge amount of air getting into the system ? Thanks

[Chris J Dixon]

Are you saying that each time you bleed you are getting lots of air, not that it is simply working its way out from where it has been trapped?

Is the pump speed significantly greater than the old one?

Has the flow direction changed?

If air is being sucked in, then the possibility is that the system is incorrectly configured, since it should mostly be positively pressurised. If that is the case, you probably won't see a leak, the displaced water ending up back in the header tank.

If you bleed with the pump running, is air leaking out or in?

Maybe a joint disturbed or renewed during the work is the culprit.

Chris

[Andy Cap]

I have removed significant amounts of air on about half a dozen occasions spread over the eight weeks. I appreciate that in the early days, the heating had not been on to any degree but by now I would have thought most of the system has been used.

I've just had a look at the header tank and though the level hasn't risen significantly, it definitely looks as if it's been pumping over by the froth on the surface, also there was heavy condensation on the plastic cover which makes me think the water is warm. I'm guessing pumping-over would add a considerable amount or air !

This replacement pump has speed settings 1,2 & 3 and was set to 2. I've altered it to 1 and will see how it goes, otherwise I can always get the guy back but I just wanted a better understanding of why it might be happening.

Thanks Andy C

[RJH]

The last time I gravity flushed my closed system it went from quite noisy to virtually silent. Only material change I made was the use of Sentinel inhibitor in place of a Wickes own brand, and a couple of new radiators with 10mm plastic pipe feeds.

[Roger Mills]

Definitely sounds as if it has been pumping over - that fits all the symptoms.

If reducing the pump speed doesn't fix it, make sure that the pump has been installed the right way round!

[Dave Plowman (News)]

Most likely cause is it's pumping over. Too much head from the pump.

[John Rumm]

As an aside, did he do a proper system flush before installing the new boiler?

[Andy Cap]

Yes he did do that.

[newshound]

A possible quick check for this, if it still pumps over on speed setting

1, would be to partially close one of the pump isolating valves (ideally the "output" one). Also, you should be able to see pumping over by looking in the tank when the heating is running.

[Andy Cap]

I've turned the pump down a notch and fingers-crossed, you're right.

[Michael Chare]

You mention that the bypass valve has been replaced.

What happens if you turn off all the radiators and start the boiler?

[Andy Cap]

I'll give it a few days, now I've reduced the pump setting and if there's no change, I'll give that a try. Cheers.

[Andy Cap]

The system's been nice and quiet now for three morning and everything appears to be functioning OK. Nice easy fix ! Thanks for the pointers.

Andy C