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A question we have been asked previously relates to how to drain a combi boiler central heating system and a typical situation is “I need to replace a faulty radiator valve and although I’ve done this job a few times before i have now had a combi boiler fitted instead of the old system with the tank in the attic. so I’m unsure if i need to bleed air from the boiler as this is the highest part of the system.”
Many times householders attempt central heating system repairs and maintenance themselves. Draining and refilling central heating systems which include combi boilers are a common challenge. This is perfectly OK provided that the gas pipework and gas heating components are not being touched as any gas installation or maintenance work should be completed by a CORGI (Gas Safe) qualified plumber.
Before you attempt to drain and refill a central heating system it is best to read how to do the task, walk through what you would do (without starting any work on your central heating system) and then start whilst taking notes of what you have done.
If you feel that this is outside your abilities then you should contact an experienced plumber before you start … taking over your failed job will attract a cost premium!
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Great answers we are often told…one more thing how do i add central heating inhibitor? The questions never end.
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Turn the boiler off. Look on the radiators and or pipework for a drain off valve and attach a hose pipe, then open drain valve. once it is draining let air into the upstairs radiators via th vent . To refill, close the drain valve, close all the rad vents and open the filling loop on, or near to the boiler and pressurise the system to 1-1.5 bar then vent the radiators and re-pressurise. Do this until you have cleared the air from the rads then check the pressure again. Keep your eye on the pressure for a couple of hours after the boiler has been running and top up as required. Most combi boilers have a braided flexible hose which connects the cold water to the heating system but some eg Worcester have a special plastic tap which operates an internal filling loop, check the manual.. good luck
You should have drain-offs on the lowest points of the central heating system so you just need to drain the system from these points. Make sure, whilst draining, you open the upstairs air vents to ensure ALL the water is drained from the system. Change the valve then add an inhibitor to the system. (to prevent corrosion/rusting) Re-fill the system via the filling loop, either under the boiler or actually built-in and bleed the radiators, most combination boilers will have an automatic air vent on so should release most of the air themselves. Let the system run and any air which the auto air vent hasn’t released will circulate to the rads, you can bleed it yourself from here. Keep your eye on the pressure gauge on the boiler whilst bleeding cos the pressure will drop and you will need to keep topping it up. Hope this helps??
There are many different manufacturers of inhibitor, i generally either use Fernox or Sentinal, you can purchase the inhibitor either in a bottle or in what looks like a tube. Although these two types are in essence the same thing they can both be used in different ways. The one in a bottle is easier if you have an open vented system (the type with tanks in the loft) when you’re re-filling this type of system you can add the “bottle type” directly to the small tank in the loft which is then added to the system as it fills.
When you’ve got a sealed system (Combi system for example) things are a little more difficult and this is when the inhibitor in the tube comes in. There is less in the tube than there is in the bottle however it’s concentrated gel type liquid so it is the equivalent of approximately one of the bottles. This maybe easier for you to use, and make sure the heating system is still drained when you add the inhibitor. With the tube type you’ll need a silicon gun, insert the tube into the silicon gun and attach the radiator attachment which comes supplied with the inhibitor. Select a radiator (generally one upstairs is best) and, ensuring the system is still drained, you’ll need to remove the air vent pin from the top of it. Once the air vent pin is removed you’ll be able to insert the special attachment which came with the inhibitor into the tiny vent hole, with this done you can squeeze the trigger on the silicon gun thus adding the inhibitor. When the tube’s empty the job’s done, ensure you replace the vent pin and you can re-fill the system as i think i explained above. Hope this helps. Any problems call the number below.
on one of your downstairs radiators you should have a drain off but if not just pop into b&q they sell a self-cutting drain-off .connect a hose a discharge into a drain then open bleed vents from top rads down to lower rads then depending on your boiler it will either built in or seperate filling loop this refills the system .also boilers have built in air emittance valves you will here this hiss when filling no hiss check the cap is not screwed down dont for get to add inhibitor go to wickes for this they sell it in a precharged can with conections for rads ect