Using a Combi Filling Loop as a Power Flush

[Pete]

I recently found that my 2yr old CB28 boiler and new central heating system never had any inhibitor chemical added to the sealed system,the water is a bit brown. I've been advised to clean the system and add inhibitor.

Once the cleaner has done its best, I thought I would be able to undo the drain plug on the kitchen radiator, and while the water pours out turn on the filling loop at the Combi boiler, thus power flushing the entire system with nice clean water.

Does this sound Ok or am I deluded.

Pete.

[Set Square]

You are deluded.

Your method will only result in flushing the shortest part from the fill point to the kitchen radiator. You need to:

• turn off and drain all radiators

• remove each one in turn and take it outside and wash it out with a hose

• with the radiator out, and the filling loop connected, open each radiator valve (with a bucket handy) and run until the water is clear

That way, you'll flush *all* the pipes *and* the radiators.

[Pete]

Thanks for putting me strait.

Ouch!! that sounds like a heavy duty job, maybe I could just add inhibitor seeing as the system is only 2yrs old and halt any further corrosion.

Or am I double deluded

Pete.

[Tim Small]

Hmm, I'm not sure this is necessary (although it is probably the most thoughrough way of doing it).

I had a similar problem - slack plumber had never flushed the system. I added a drain valve on the return to the boiler. On my boiler, when it is turned off, no water can flow from the fill point to the drain (i.e. through the boiler heat exchanger). By fitting a bit of garden hose to the drain point, closing all rads off, then opening each in turn, I believe I was able to flush just about the entire system, without disconnecting any rads..

Tim.

[Andy Hall]

... and narrow :-)

It really depends on how bad it is. A system without inhibitor can be quite full of sludge in a matter of months if the tap water is aggressive.

The proposal from Mr Set Square gives the right angle on this and I would take that trouble if the system is microbore or there is any sign of radiators feeling cool at the centre bottom when the heating is on. This is because sludge build up in radiators tends to be at the centre bottom. If it finds its way into the pipework, the flow will become a problem.

Since you're depressurising anyway, then you could do a sample of one upstairs and one downstairs radiator and decide from there. If it isn't bad, then John's method works well as long as you have the service valves and can direct the flow.

You can also add a system flushing agent (Fernox and Sentinel make them) and run the system hot for the recommended time - normally up to a week. Then thoroughly drain and flush and add the inhibitor. Chemical flushing agents won't clear a heavily sludged system but will help if the problem is fairly minor.

.andy

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[John Stumbles]

You can get a more thorough flush without going to the lengths of individually flushing each rad by judiciously turning off radiator valves and service valves on your boiler to force the water to go through other paths. You'll need to know how it's all plumbed together to figure out how to get it to do what you want. And/or you can just run it up to full temperature then switch off and open up the drain c*ck to empty it; refill and repeat a few times.