Flushing frequency of central heating systems

Thanks. I had already found a copy. The wikidiy article is effectively a copy of the British Standard.

Many thanks for the link - most helpful article.

For DIY, might it not be most effective to just remove the radiators and give each a good flush with a hose? It's what I ended up doing here. Not sure how effective it was/will be, but the (sealed) system was filthy.

I had thought about doing that, except unless you are extremely careful, you may find the radiator deposits a dose of black sludgy mess all over the floor when you uncouple the fittings.

Also upon refitting, you may well find you have a leak or two, or three.......

Ere, do you mind :-)

As it says in the intro "There is a British Standard document (BS7593:2019 Code of Practice for treatment of water in domestic hot water central heating systems). Some of this document is based on the previous (2006) version of this standard"

However there is a fair amount of additional info in the article...

The header is open to the air, and the system connected directly to the header by the feed and expansion pipe. (and there is also a vent pipe that is open to the air).

So in normal operation it will push water into the header, and then suck it back again as it cools. So some fresh oxygen will get in each time.

Are there any advantages in having a header-tank CH system rather than a pressurised one? I've only ever had pressurised ones. I tend to think of header tanks (either for hot water or for CH) as something from pre-history ;-)

Can I assume that you are the author of the wkidiy article?

If so, many thanks, it put me on the right track.

Fair to say that one was mostly mine (ISTR doing that after I flushed my system when I put the boiler in - had some photos, so thought I might as well find a use for them!)

(if you click the "view history" link on any article, you can see who has contributed to it)

Glad it was useful... I might go reword a few bits at some point - it is a bit repetitive in places.

Not especially... it is much easier to add dosing chemicals though.

ISTR there was a time that sealed systems were forbidden by water regulations in this country (presumably because of the risk of back contamination of the mains supply). Early 80's rings a bell... That would also tie in with when we first had CH installed at home - I remember coming home from college one evening to a warm house for the first time! One of the installers commented that the sealed system boiler they had installed had only recently been permitted.

Hence the modern requirements for things like a double check valve in the filling loop, and the (typically) removable hose. There are also additional requirements for the overtemp/pressure release valve.

Yup, I would concur :-)

I still have the DIY central heating book I followed to install my central heating. It doesn't even mention pressurised systems, only open vent.

The book was published some time in the 1980s - there is no date of publication in the book but a quick google suggests the later updated version was 1989.

The book seems to suggest that balanced flue boilers were just starting to become more popular.

I fitted a balanced flue boiler in out last house in the early 1970s. Pre- natural gas.

Is this the page you're referring to?

I once had a central heating header tank in the loft which furred up with lots of mould or bacterial growth.

There was inhibitor in the water. I wonder if it was too concentrated and actually caused this. I would pour it into the header tank to top up the system.

Yup

I've just had my water bill, 50% more usage than for the same 6 months last year! Metered.

Anyone like to hazard a guess how much water was used, full on tap, good pressure, for ~5hrs?

Didn't occur to me to take a "before/after" reading and can't think of anything else to account for the difference.

Pressure isn't the only important parameter -the diameter and length of the "pipe" (hose and/or metal) matter. With my metered garden hose, it can range between about 500 and 1000 litres/hour. On that basis, around

That's about what I would have thought. But that doesn't seem to stack up with the OP's comment about a 50% increase. If 5M^3 represents a 50% increase in consumption over a 6-month period, the baseline consumption must be exceedingly low! But that doesn't take account of the standing charge.

My standing charge is equivalent to about 25 M^3 of consumption per half year so, if the bill including standing charge, is up by 50%, that could represent an addition 12.5 M^3 or so.

What were the actual consumption amounts for the 6-month period in question, and the equivalent one last year?

Hence I stated consumption and not cost.

It's gone from 40m^3 to 60m^3. The flushing is obviously a significant factor accounting for 1/4 of the increase perhaps. I need to investigate/monitor more. I don't think we had much summer watering.