How to put anti-corrosion stuff in central heating system

[405 TD Estate]

Hi - first thanks to everyone who posted on my topic how I drain my central heating to fit new radiators -

Now if I get this done how do you put corrosion inhibitor into the circuit - which brings me onto how does the circuit work - does it take how water from the cylinder (my heating is 20-30 years old maybe more) and if so how is the inhibitor kept seperate from the hot water?

[Roger Mills]

If you've got a conventional vented system, you should have 2 tanks in the attic. The big one is the cold header tank for the domestic hot water and the small one is the fill and expansion tank for the primary circuit. The primary circuit consists of the boiler and radiators, and the indirect coil inside the HW cylinder which heats the DHW without mixing with it. You can thus put inhibitor in the F&E tank, and it won't get into the DHW (unless the HW cylinder is faulty!)

If you're unfortunate enough to have a Primatic (or is it Fortic?) cylinder, a single header tank is shared by the primary and secondary circuits, and limited mixing takes place. In that case you're stuffed, and can't add inhibitor to the system. The best solution is to replace the cylinder with standard indirect (fast recovery) cylinder along with separate header tanks - or even convert the primary circuit to sealed/pressurised if your boiler can cope with that.

[Stuart B]

If it is similar to the setup I had before I got the new CH Boiler then the water in the cylinder will be heated when the hot water from the boiler passes through a coil which sits within the cylinder,the domestic hot water being taken from the top of the cylinder ....The CH water and the Domestic water remain totally seperate .

I now have a filling point just below my new boiler which makes adding inhibitor easy . I have seen suggestions previously in this Group to add the inhibitor via a radiator by draining the water a bit then adding the inhibitor via the bleed plug . My old system had a Primatic cylinder so I couldn't add inhibitor

Others will no doubt respond with more suggestions . If you Google for something like "adding inhibitor to radiators" then I'm sure you'll get answers as well

Stuart

[David Hansen]

On Thu, 20 Dec 2007 08:21:32 -0800 (PST) someone who may be 405 TD Estate wrote this:-

That depends on how the system was designed and installed, which is something we cannot determine from our keyboards.

However, it is likely that your system has a separate heating circuit which does the central heating and heats the water in the cylinder, fed from a small tank in the loft. This is entirely separate from the domestic hot water (and perhaps some of the cold water fittings), fed from the large tank in the loft.

You should first flush out any installation debris. Then you should circulate a cleaner for a while. Then you should flush this out. Then you should introduce the inhibitor. Both can be introduced at the small header tank. Drain off some of the water first, then put the chemical in the tank, then fill the system.

There are instructions on most bottles of both.