boiler inhibitor

[nellwood]

How do i add a boiler inhibitor to my boiler, i know you have to drain down somew of the system but could someone tell me in detail

many thanks nigel

[buildersmate]

It depends whether you have a pressurised system or not. If it is unpressurised and has an expansion tank in the loftspace (the little tank next to the big cold water tank) you can add the inhibitor into the water in the header tank. It will circulate itself gradually as the water gets pulled / pushed in and out of the tank by expansion. Or you could speed up the process by shutting off the ballvalve to stop more water refilling the tank, then bleeding one of the radiators to remove about five litres of liquid that you tip back into the tank. If the system is pressurised the procedure is different. The usual route is to close off one radiator both ends, remove the bleed valve to enable the removal of about 500ml of liquid by sucking it out, then refilling with the concentrated inhibitor. This comes in tubes of about 400ml. Look out for Fernox or Sentinel. Both products come with full instructions and a little kit of adaptors to be able to do it.

[Tim B]

(unpressurised) Another answer is both simpler and more complicated. You need to know the approximate capacity of you system because you have to add the inhibitor at a specific concentration.

Is there already an inhibitor in the system? Your new additive might not be compatible with the old, check the label.

Calculate the amount of inhibitor that you need to add. Turn off the boiler. Turn off the rising main or supply to the header tank. Drain off all the water, turn off the drain. Add your chemical to the header tank and it will flow to the lowest part of the system (this will ensure that the additive gets to all parts as soon as the pump starts) and turn the water supply back on.

When the header tank is full turn on the boiler, sit back and bleed you rads as necessary.

[buildersmate]

A normal size 4 bedroomed house will have about 90 litres of fluid. The manufacturers know this and produce a container of a size that is adequate for 100 litres. One bottle (or 400ml tube if in concentrated form) normally does it.