Central heating air vents

Rollinghome

We had our old gas boiler replaced a couple of weeks ago with a new open vent regular boiler. I was a bit surprised to find our Magnaclean filter choc a bloc with sludge less than a week after the system was supposed to have been power-flushed and a radiator not working. So we're having them back next week to have another go.

Was also surprised to find that they had removed the existing vent pipe, and we now have four vent caps dotted around the system and just a feed pipe from the header tank.

I can understand that it's easier and cheaper to have a combined feed and vent pipe, but is it common to remove an existing vent pipe?  We never had any problem with air in the system previously or airlocks when refilling the system so seems an odd modification.

Like this.

ThisIsWeird

Rollinghome said:

We had our old gas boiler replaced a couple of weeks ago with a new open vent regular boiler. I was a bit surprised to find our Magnaclean filter choc a bloc with sludge less than a week after the system was supposed to have been power-flushed and a radiator not working. So we're having them back next week to have another go.

Was also surprised to find that they had removed the existing vent pipe, and we now have four vent caps dotted around the system and just a feed pipe from the header tank.

I can understand that it's easier and cheaper to have a combined feed and vent pipe, but is it common to remove an existing vent pipe?  We never had any problem with air in the system previously or airlocks when refilling the system so seems an odd modification.

Like this.

Hi Rollin'.

I'm no expert on such systems, especially vented ones like yours. I gather, tho', that it's ok to combine the feed and vent pipes into one, and this should do the job of both - with some provisos, like a min pipe size (22mm), and - of course - that it's been done correctly. Nothing to suggest that there's anything wrong with yours.

If the 'existing vent pipe' you are referring to is the one that goes up into the loft, and arches over the small F&E tank, then that serves a completely different purpose to these wee vents you've shown there (tho' it also dispenses air bubbles flying through). The F&E tank supplies your system with water, acts a top-up reservoir, and also captures any over-heating flow ejected out that vent pipe. From a Google, it seems it's perfectly fine to combine the feed and vent pipes into one - on more modern boilers with overheat 'stats.

So, chances are, that's all fine, and you can ask them for clarification, now you have the info.

The wee vents you've shown in your pic are different - these are to allow pipes to be 'bled' of air, either when refilling the system, or just to keep it in good order and avoid air locks in use. They look like 'manual' vents, so you need to slacken that knurled top cap each time you want to vent a pipe. I'm guessing that they were put there as a 'just in case', perhaps because they spied lengths of near-horizontal pipe, which can be prone to airlocks? Could you show some photos of them in situ, please? Are there short vertical lengths of pipes coming off the main pipes to these vents? If so, that would be to capture any air running through your system, and it'll remain there until the vents are opened to release.

Of more concern is the seemingly less-than-ideal system clean! Did they do a 'powerflush' - did they have a machine that looks a bit like a hoover that actually pumped water around the radiator system? And a large magnetic filter to capture the resulting sludge? Or did they just do a 'chemical' clean - ie add strong cleaners, run the boiler for a half hour, and then drain?

Old systems, especially vented ones, are prone to having sludge build up if not properly maintained, so it's no great surprise that yours is like this. It's also quite common for settled and compacted sludge - which can sit in the bottoms of your rads relatively benignly - to now be released, and get into the system water. But, yes, you do want all that removed for your new boiler - or the vast bulk at least, and then the mag filter can carry on capturing the rest.

Rollinghome

Hi TIW,

Yes, as you say, it is quite common now and in a new installation running just one pipe saves time and money.  But I don't really see the sense in removing an existing vent if it's properly positioned, or in creating potential air pockets needing manual bleeds. I've installed a few CH systems in our previous homes myself (a good while back when boiler regs were more lax) and always tried to avoid problems in the first place rather having to put extra in extra bleeds to deal with them.

Yes, it was supposedly power-flushed, but anyone can hire a machine for the day, and the results depend on how it's used.