Flushing central heating radiators.

Project88 · 25 Apr 2007

Hello,

Question first, story afterwards if you are interested

Any tips on the best way to flush central heating radiators. The boiler is broken and the system is totally drained, so no chance of pumping anything around the system. Obvious answer is to remove each rad take it outside and shove a hose pipe up it. But which hole is best :shock: Inlet, outlet, bleed hole? Or does it not matter?

Short story of events.
My old, until recently, reliable car started to give the signs of expiring, so decided it was time for replacement. Chose a shiney new Peugeot 207. Did the deal and on the day of purchase was emptying the old car bits into the garage/workshop. Noticed some water in the workshop rubbish bin :? Then noticed the drips hanging from the bottom of the boiler, then noticed the water stains on the full sheet of 18mm ply :evil: then noticed the hugh wet patch on the floor under the MDF which was stacked on edge :x
Had no choice but to leave it all soaking whilst we went off to hand over the cash and get the new car, boy was the shine taken off of that experience.
Anyway boiler is 17 years old and a write off (verdict of 3 separate plumbers). So more money on a brand new unit. Amazing experience here as well. Ended up with 4 quotes, all from Corgi registered local plumbers, the dearest was well over double the cheapest. The job is very simple old boiler off the wall, new boiler on, few pipe connections, new drain pipe, that's it. One to one and half days work, the high quote effectively charged £1400 for labour :shock: Nice work if you can get it.
So I will flush the system before the new boiler goes on, hence the question.

Any comments gratefully received.
Cheers,
John.

OLD · 25 Apr 2007

Hose in outlet with open inlet when i did it to a partial blocked rad it failed one month later and had to be replaced the muck must have sealed it.

Nigel · 25 Apr 2007

Check with the plumber putting in the new boiler as some manufacturers insist on a full system flush with chemicals when fitting a new boiler to an old system or they will not guarantee the boiler,

Nigel

Woody Alan · 25 Apr 2007

It's not easy to "flush" a heating system as a DIY project. If you really mean flush in the sense of the word then the proper way to do it is with a pump and vortex container purpose built for the job. Connect the unit at the boiler flow and return (disconnect boiler to acheive this) assuming CH pump is in boiler, I'm not sure how much significant resistance the pump has if it's in the circuit. Anyway, it's usual to put a cleaning acid in the water that you want to clean out the system with. How strong an acid is debatable, too strong and you might find leaks you didn't know you had. To direct the cleaning open the zone valve to raditaors and generally pump through, to claean an individual rad open lockshield and valve wide and close down all other rads, run pump, reversing flow direction now and then to unsettle things. The waste should settle out in the vortex of the unit. If you can't get the proper equipment the only alternative is drain down fill up with cleaner close all rads bar one and put pump on full repeat for all rads drain down and repeat until the drain down looks clean. I AM NOT A PLUMBER OR CENTRAL HEATING EXPERT!

that may be obvious alredy

Dave S · 25 Apr 2007

I've done this a couple of times, based on advice I got on a DIY newsgroup.

Normally I've done it with the system still full.

- Since your system is drained, I would check the header tank. It may well have a load of crud at the bottom, in which case I would disconnect the tank and clean it out, otherwise much of the crud will end up in the system when you refill it.
- Close off both valves on a rad.
- Place shallow trays (cat litter trays work well)/polythene etc under rad - the dirty black water from the rad will badly stain a carpet.
- Undo the valves from the tails. Catch as much as you can in the drip trays, then use rubber band to put polythene bags (eg freezer bags) over the tails to catch any drips while you remove the rad.
- Take rad outside, remove tails then use a pressure washer to flush out the rad. I've found a hosepipe to be of little use in removing sludge. This is a pretty wet and messy operation.
- Indoors (this stage you can't do as your system is already drained) open a valve and flush through until clear water comes through. Repeat with the other valve.
- Replace the radiator and connect up.
- Repeat this with all radiators.
- Tie up ballcock to header tank so that it doesn't refill, then drain off enough water from the system to more or less empty the header tank.
- Put most of the recommended amount of anti-corrosion into the tank and release the ballcock so that the tank refills.
- Put the last cup or so of anti-corrosion into the header tank to help prevent anything growing.

Of course, in your case, the refilling will be done by the plumber when commissioning the boiler. Afterwards, prepare to be bleeding air from the rads a few times in the first few days and probably a couple of times over the next few weeks.

Two pieces of advice based on experience: I wouldn't consider moving radiators without wearing my steel toe capped safety boots. Radiators are heavy and are a quick route to amputation if dropped.
Also, if you don't have a pressure washer, I would consider buying or borrowing one, or failing that perhaps renting one. Considering the extra sludge I got out of a radiator with a pressure washer having already flushed it with a hose, as well as the hassle involved in doing the whole process again, I consider it a good investment. I think there have been some threads about pressure washers on the forum, but my own which cost about £40 IIRC was certainly up to the job (and many others). In the context of the costs of boiler replacement it's next to nothing.

HTH

Dave