Condensing boiler

[Yorkie]

A further question, what is you opinion on boiler and system flushing equipment and methods?
Bear in mind that whatever happens the system will be opened up this summer. Cylinder will be removed (and opened) to fit solar coil.
Pipework will be open as I will be tidying up and re-positioning the manifold and motorised valves. It would even be quite easy to take the boiler right outside to flush it.
System has been run with inhibitor since new, some trace of black gunge when a radiator has been removed and some kettling in boiler now, but no real gas/air in system problems (one particular red will need bleeding every 4 months)

Thanks, Ed
Ed

When a new boiler is fitted, ordinarily, it's a requirement to 'powerflush' the system. The equipment consists of a powerful pump which pumps clean water through the system and drains off the sludge that may have collected in the radiators over the years. Obviously it's not good practice to fit a new boiler onto a sludged up system.

That said, 'powerflushing' has gained a bad name, and not without some justification, as it's often used as a 'make-work' moneyspinner (not least by certain large outfits who will remain nameless), with gullible customers who are told, and believe, that they should have their system powerflushed to make it more efficient, even though there are no signs of problems, such as some or all radiators not getting hot when the circulating pipework is.

In your case Ed, since the system will be drained down anyway, if you want to do a thorough job, although it would be a bit of a pain, you'd be just as well to remove each radaitor, take it outside and flush it through with a hose. Turn the radiator upside down, fill it with water, then turn it upright to let all the gunge drain out. If you do that a couple of times with each radiator, they should come nice and clean.

On the face of things, pressed steel radiators mght see the worst material for containing water - they'll rust won't they? No they won't, and no they don't! When a system is filled with fresh water it contains oxygen, but this is soon dissipated and in so doing, will leave a film of oxide (rust on the inside of the radiator, and that's it. Once the oxygen has done its worst, there will be no more in the system unless and until it is drained off again. That said, it makes sense to apply rust inhibitor to the system each time it's filled. Most systems do have minute leaks which go unnoticed - at radiator valve glands for example. Ths is why on presurised systems (which only operate at about 1.5 Bar - 21PSI) often lose pressure over time, and need re-pressurising by opening a valve on a neaer the boiler, observing the pressure gauge on the boiler util its is the correct pressure - a simple taks for householders to perform, and another lucrative money-spinner for those who have a combi boier and find that it's shut down. Along comes the 'service engineer' and does what the customer could have done. £35 for five minutes work - easy life!

If people are in the habit of removing radiators to decorate behind them or have alterations to the system which call for it to be drained down, that introduces fresh oxgenated water, so they system should be treated once more with inhibitor.

When you've done the work Ed, fill up the system without inhibitor, and bleed the radiators. Check for leaks, then open all the radiator vents and drain the statem down to flush it. It you're conscientious, allow the system to come up to temperature, and after running it for an hour or so, drain it down again to rid it of any flux or grease which the hot water will have melted. Then fill up and put inhibitor in as directed in the instructions. (You want it in the system itself - not in the expansion tank, so it needs to go into the tank before the system is full).

As to saying that 'one radaitor will need bleeding from time to time' often it isn't air in ther system, but hydorgen from hydrolysis of the water. You can easily check that by holding a cigarette lighter to the 'air' to see if it ignites. If so, it's hydrogen of course. You can get automatic bleed valves which are very cheap simple devices. Basically, they have a little plug inside which - if it dries out will shrink and allows air to bleed from the system, then as soon as water comes into contact with the plug, it swells and stays swollen till more air/hydrogen makes it shrink again. Neat eh? You might find that when you've fully drained and flushed the system and filled up including inhibitor, that the problem goes away.

Hope these additional pointers are of interest and help Ed.

Best of luck in your endeavours!