Flushing central heating systems

Since it has come up a few times recently, and I had a couple of photos handy:

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welcome as usual.

Reply to
John Rumm
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In article , John Rumm writes

Powerflushing

No. 4, should that be tapping rather then tripping :-?

Mains pressure flushing

Maybe add a warning to control mains flow such that pressure doesn't go above 3 bar and pop the over pressure relief.

Reply to
fred

Yes, well spotted - difficult to trip a rad - they don't normally walk far!

If you have isolated the boiler, then the PRV will normally be "out of circuit" during the process - still on sealed systems that are "assembled from bits" this might be worth keeping in mind.

Reply to
John Rumm

I thought it might be a sixties ref to Lucy and psychedelia.

Yes, my system is home grown and has the PRV just outside the box on the flow side. I only have the boiler isolated (well, flow stopped) on the return side as you can't really get muck in if there's no flow through. I never bothered with full isolation as it's only a little extra water to drain down if needs be. I think there's a requirement for an uninterruptable path between boiler and PRV (no problem if it's internal) and I didn't have the space on that pipework to fit PRV, fill point and a further isolator after that.

Reply to
fred

What would be a reasonable quote/cost to flush an 8 radiator with combi boiler system.

Reply to
Bob H

Na, my 60's memories are very poor ;-)

I added some words to accommodate such systems...

Reply to
John Rumm

Short answer is, I don't know. I know doing my system (21 rads) via the mains flush technique took about 3/4 of a day to do well[1]. So perhaps half a day to do a proper job on a 8 rad system. Convert that into typical day rates in your area, and add cost of chemicals. Seems like £200 would be a starting point.

[1] Its also surprisingly knackering by the time you have walked back and forth to each rad about six times, and fiddled with valves at floor level!
Reply to
John Rumm

Some guidance on frequency...

A sealed system with inhibitor which never or rarely needs topping up or bleeding can run for many years without draining. (I've gone for 7 years, and the inhibitor was still working and the water clear.)

Vented systems and sealed systems which need regular topping up will lose their inhibitor, and if it's not topped up, they will sludge up.

Bleed a little water out, and if it's dark, that's a good indication that the system has seen some corrosion, and should be drained and refilled with inhibitor, or flushed if very dirty.

When draining a vented system, the header tank can have quite a crust of floating sludge. Skim this off using a jug first, so it doesn't get washed into the pipework.

Be prepared for drain valves that a) won't open, and then b) won't close. ;-)

I was lucky I had bought an Aldi plumbing washer set a few weeks before I drained down a friend's system, as the remains of the rubber washer in the drain c*ck washed out with the black water.

Reply to
Andrew Gabriel

Ta, looks good.

Reply to
fred

My parents' system had a Primatic cylinder and the boilers were changed from solid fuel to oil, then to gas over the course of nearly 50 years without being flushed and probably without inhibitor. The stuff that came out of the radiators when they were bled once or twice in the 30 years that I can remember was certainly rather black and like a suspension of graphite. I believe it was flushed and had inhibitor added when the Primatic and boiler were replaced by a gas condensing combi-boiler a couple of years ago and has worked fine since, without leaks.

Reply to
Martin Crossley

+1

Surely you're not going to tell us that little lot has come out of

*your* system, Mr Rumm?!:
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Reply to
Lobster

Is there any significant difference of interpretation between it being blackish or rusty brown?

Reply to
polygonum

50+ year old radiators were much thicker and designed before inhibitors were used, and expected to last the life of the building, and for the most part will still be fine even if no inhibitor has ever been used.

For anything newer, this becomes less and less true, and any bought in the last 10 years will have a very short life if no inhibitor used, and even if it is, you are most unlikely to get anything like 50 years out of them.

I can see this in my parents system which was installed by dad in 1959. All the original radiators are still fine. Radiators added in 1967 lasted 25-30 years. Radiators added in the mid 1970's lasted 20 years. A radiator added in 1990 lasted 5 years. Since 1998, the system has had inhibitor added (due to a new boiler), and only one more failure which was a new radiator a couple of years before the inhibitor was added.

I could probably plot a graph which would show something like any radiator bought before 1965 would last forever, and any radiator bought after 1965 would die by the year 2000, without inhibitor.

Reply to
Andrew Gabriel

My parents had CH installed in the mid-60s when I were a lad, and mum still lives there; I'm pretty sure all the original radiators are still present. Maybe time she moved!

David

Reply to
Lobster

And that was with regular dosing with inhibitor, and treatment with descaler/boiler noise reducer!

Although its probably worth pointing out that was only regular for the 4 years I owned it - what happened in the previous 20 odd is anyone's guess - although I have a suspicion it did not get much in the way of love and attention.

Even with a bit of tweaking under my stewardship it still pumped over a little from time to time. The system was also inappropriate for the property, since it was vented, but really had insufficient head which made it rather too easy for it to suck in air from time to time. So I was not expecting it to be pretty.

So there was plenty of black water as you can see. I was directing it into that basin tangentially - so it tended to spin the water, which was quite handy because it dropped most of the heavy stuff in the middle of the basin (the plughole is to the side) which made it easy to see how much heavy stuff was coming out. As I could get plenty of flow rate through it, most of the fine stuff lifted and flushed quiet easily. There must have been the equivalent of a few cupfuls of heavy particulate / magnetite observed though.

To clean it I chucked in a couple of litres of cleaner, and left that circulating for a week or so. Then I drained down and capped off the vent and feed pipes. Then flushed everything as described, doing one rad at a time until each rad ran nice and clear (remembering to open the valve on the next before closing it on the previous one - so you don't accidentally try and take the whole system up to 5 bar!). I then reversed the flow direction and repeated the whole process. That shifted a surprising amount of extra stuff that I was not expecting.

Later I set about rad juggling / upgrading as required, so got a chance to take a few rads right out of circuit and flush them individually to see what had been missed. The answer being nothing of note, so I was reasonably confident the rest of the system was clean.

Since the new system has been running I have checked the TF1 after a couple of months. The water it had in it was discoloured a bit but not too bad. It had also trapped about a teaspoon of particulates and magnetite

Reply to
John Rumm

Yup good point - pinched that ;-)

Reply to
John Rumm

Including those fitted in 2001? ;-)

Reply to
Mark

Just treat them as consumables... :-(

Reply to
Andrew Gabriel

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