Constantly having to bleed rads + dirty water in new rads

[zzz]

We had renovations a few months ago (maisonette flat, 8 rads). Before that, 3 rads and boiler were new (3yo), the rest ancient. But all working fine - got very hot quickly, only occasional bleeding needed, water came out clean during bleeds.

Now with 5 new rads added... I have to bleed every few days, loads of gas comes out (upper floor rads). It's been weeks since CH went on, surely there's no way that should still be air trapped during the system refill when the work was done? I tried trapping the gas in a cup and lighting it as I read online - does not pop, so does that mean air is getting in somewhere rather than hydrogen from corrosion? But I see no leaks anywhere!

Second thing - when water splutters during bleeds it's really dirty with black particles (see pic). As it seemed clean before the renovations, and old rads which may have had sludge at bottom were removed, is it normal for an essentially new system to be so dirty?

How can I hunt down where air is getting in?

And is it worth paying a plumber to empty and refill the system (and maybe add inhibitor and sludge remover, or a filter)? Boiler is due for annual service this month anyway. I've read on here that power flushing is not the best use of money...

Many thanks

 

[ianmcd]

make sure the system is switched off when you bleed the radiators, you dont want the pump running as you bleed them, your pic does show some contamination, but perfectly normal to be honest, so much is made these days that system water should be like unicorn tears

 

[Madrab]

The best trick I find is to bleed the radiator into a glass and see how clear the system water actually looks once it settles, do you have a mag filter installed? If you are having to continually bleed then it's either making gas (which you've tested for) or it's losing water, can't be anything else.

I'd now be looking for leaks. How regularly are you having to top up?

Was there inhibitor added to the system when the new rads went in?

 

[zzz]

Thank you both.

It would be difficult to bleed into a glass - they are "designer" rads and bleed valves are on top, with a little air escape hole pointing upwards. If I let water flow out of it, it would run down the side of the rad and make a mess.

Do have a Mag filter fitted. Don't know if the builders added inhibitor, will have to ask.

Sorry if it's a stupid question but is it possible for air to be sucked into the system without water escaping at the same time? Or to be sucked in at the boiler not the pipes? The builders left the boiler at almost 2 bar on the pressure dial back in July, I just checked and it's down to just below 1. That's a big loss of pressure but the only time something similar happened was a long time ago when a rad valve leaked and I had to have a bowl under it and empty it once a day until the plumber came. And had to top up the boiler with fresh water every few days. But to drop from 2 to 1, a big amount of water would have to be lost, no? I have checked all the visible pipes in the flat (all external) and see no leaks. Have just looked under the kitchen cupboards, nothing. The only places left concealed are behind the bath panel (but a leak there should show up as a stain on the kitchen ceiling), and one side of lounge where they are boxed in with MDF - but that much water loss would have surely made it swell and show a stain...

 

[ianmcd]

But to drop from 2 to 1, a big amount of water would have to be lost, no? I have checked all the visible pipes in the flat (all external) and see no leaks. Have just looked und

No not really, you would be surprised how little a volume of water it could be , all depends on your system , what boiler do you have ?

 

[zzz]

No not really, you would be surprised how little a volume of water it could be , all depends on your system , what boiler do you have ?

Not a big one - WB Greenstar 30Si Compact. The system then has 5 X 470mm x 1600mm double panel rads like this https://www.bestheating.com/milano-...er-radiator-472mm-x-1600mm-double-panel-64465 , 2 X 635mm x 650mm single panel ones, 2 small towel rails in bathroom and toilet, and a single panel 300mm x 1600mm vertical rad. So 10 rads of various sizes (I miscounted in my original post!).

I'm just so darn puzzled that I have to bleed regularly, and a lot - yet can't find a leak!

 

[zzz]

I just found this post... https://community.screwfix.com/threads/sealed-system-drawing-air-in.126915/#post-1498675 I wonder if I could have this issue and air is being sucked in via the pump ... Or as someone else suggested on that thread - via the expansion vessel. (I am out of my depth talking about boiler components though!).

The builders said at the time, in July, that they did a pressure test (at 6 bar if I recall correctly), and found no leaks.

 

[MeldrewsMate]

No leaks, but the pressure keeps dropping and there's lots of 'gas' accumulating.
Have you looked at the external pressure relief pipe? It'll probably be directly below the boiler and visible from outside as an open pipe. Is that dripping or wet from an intermittant drip?
The only other way the pressure can drop is if the expansion vessel is failing (but by now it would be obvious), there is a leak (somewhere), the boiler main heat exchanger is perforated, or the pressure relief valve is passing.

You seem to have discounted a leak, and I've discounted a failed exp. vessel.
What is the system pressure when the boiler and rads are cold? What is it when they're up to temperature?
Is the boiler at the highest point in the system?
Does the boiler run more noisily when cold than when hot?
Have you checked each rad valve AND each valve gland (damp/wet under the cap)?

The disturbance of the pipework and rads during the boiler change will have released some silt back into the system. Your new boiler pump may well pump better than the removed one, and thus more silt will be lifted into circulation. Your mag filter should catch this, though it's worthwhile cleaning the filter thoroughly and then checking it a week later - this will give you an idea of the amount of cr*p in circulation. As said, dont get too hung-up on its colour as long as all parts of all rads are getting hot.

You have my sympathy with that boiler. Nothing in there is easy to get at!