Flushing rads + heating systems - valves on header tank?

[David Robinson]

I want to flush my heating system using mains water.

Problem is, in a vented system, it'll all just spray out into the loft.

FAQ says disconnect the feed and expansion pipes from the tank, and connect them together. Hmm - don't like disturbing connections to plastic tanks - especially when I didn't make them - they have a habit of no going back properly and/or weeping.

So, I was wondering if I could put a valve in the 22mm feed? I could put one below where the feed + expansion splits, or I could put two in

- one for the feed, one in the expansion.

Now, I realise that if anyone shut these valves and then turned the heating on, the expansion of the water would make something split/ explode somewhere. So I was thinking maybe a 1/4 turn lever valve in the feed (convenient to turn off in the even of a leak), but a valve which can only be operated with a screw driver in the expansion pipe - maybe with the screw head filled with paint after I've finished.

What do people think - too dangerous due to risk that someone still comes along later and turns it off?

Also, in the FAQ it talks about turning the valves off at the boiler when flushing to stop the water short-circuiting through their. I can find any valves, and don't really want to fit any there - might they be inside somewhere? Sorry for stupid questions - it's a(nother) thing I'm doing for the first time.

Cheers, David.

[Cicero]

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If all downstairs radiators have drain valves you can do a satisfactory flush without any complicated method. First drain down completely, by draining through each downstairs radiator. Now fill up with clean water via the header tank and leave the cold supply to the header tank full on. Next drain for a few minutes through each downstairs radiator in turn leaving the supply from the header tank to keep the flush going. When water runs clear drain down again completely and then fill up adding inhibitor.

Cic.

[S Viemeister]

How do you dispose of all that contaminated water? We have a septic system - I wouldn't consider pouring all that stuff into it.

[newshound]

It's rust (plus inhibitor). Do you consider carbon dioxide to be "pollution" too?

[S Viemeister]

Septic beasties can be picky about their food. I don't actually know what the ingredients are, in the inhibitor in my system.

[Cicero]

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A septic system is the exception rather than the rule, I think, so obviously the owner decides how to use it.

I've never heard of any constraints on draining a domestic central heating system directly into the foul drain either because of the contents or the extra volume from flushing. In fact from time to time there are reams of advice in this NG on clearing blocked drains with such chemicals as caustic soda etc. and nobody seems to be concerned about any possible ill effects from those on the sewerage system.

A little bit of 'googling' produced one possible source of information:

in this item there is confirmation that 'trade effluent' is quite legal in public sewers (subject to conditions) so it would appear that discharging the contents of a domestic central heating system is not going to be a problem.

If there were any restrictions on this practice I think that it would be general knowledge and would have been mentioned many times in discussions on CH maintenance. If you do know of any restrictions you would be doing a service to everybody by quoting them as there must be thousands of systems drained every day directly into domestic sewers.

Cic.

[S Viemeister]

I'm in Scotland, in a very rural area - septic systems are not uncommon here. I'll prowl through the reference you provided, but after a quick scan, I didn't notice anything that would apply to disposing of CH fluids in a septic tank.

[A Plumber]

It can be drained onto the garden without any problems, that's where mine goes

[<me9]

Don't know about septic tanks, but a small sewage farm at work was malfunctioning. It turned out to be a leak in the Gent's, resulting in over

10x the throughput of water without the usual added solids. This flushed out all the bugs that normally digested the solids, resulting in the 'solids' building up and blocking the system.

So just water can upset the system.

Fixing the leak (which had slowly built up over years (from checking the bills)) cured the problem in weeks.

[S Viemeister]

Any noticeable effects on the vegetation?

[David Robinson]

Genius. Will try that.

Might not got much pressure through the upstairs rads to clean them this way since the feed to upstairs goes downstairs first, splits, and then returns upstairs.

No septic system here.

Any thoughts on the original question about adding valves, or not, to feed and expansion?

I've thought of a danger-free solution: add valve to feed, and just pop a push-fit end-cap over the expansion while flushing. Remove when finished. No danger of anyone shutting off the expansion pipe later.

Cheers, David.

[Cicero]

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I'm glad you like my suggestion.

I think it would be unwise to put in any valves which could lead to future confusion for yourself or any later owner. However your suggestion for a temporary pushfit endstop on the expansion pipe seems a good idea - perhaps it's how it's done when power flushing. I think it's unlikely that you will get much extra flushing power by mains supply using a hose pipe, given the rather convoluted pipework of a CH system.

The method I suggested would really be quite adequate for flushing out after a chemical clean. In theory at least a chemical cleaner should dissolve any sludge so that it's suspended in the water ready for draining out. Strong flushing (e.g. power flushing) shouldn't really be necessary except in extreme cases.

If you feel that your system is sludged up I would suggest that you try a chemical cleaner first and then flush as I suggested. Most of the cleaners (Fernox etc.) on the market do a really good job for all but the worst cases, and it's much easier than removing all the radiators to flush outside in the garden.

Cic.

[David Robinson]

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Thanks.

I tried your suggestion yesterday and it seems to work really well.

Very glad I put drain valves on all the rads now! I didn't expect them to be so useful so soon.

It's a new system (apart from a few pipes runs I re-used), so there's no major gunk to get out. I'll do the chemical cleaner anyway.

Cheers, David.

[John]

Thanks.

I tried your suggestion yesterday and it seems to work really well.

Very glad I put drain valves on all the rads now! I didn't expect them to be so useful so soon.

It's a new system (apart from a few pipes runs I re-used), so there's no major gunk to get out. I'll do the chemical cleaner anyway.

Cheers, David.

It is quite satisfying to take a radiator outside for a good flush. I normally do it when I decorate. Wash the back, a rub down with wet&dry and then careful repaint whilst it is lying flat on the dining table. Then refit it - trying not to mark the paint which might be still a bit soft. Whilst it is off - flush a bit of water out of the tails to remove any crud that may have settled.