by Dave From Leeds »
Fri Apr 02, 2010 1:29 am
It would appear to me that you most likely have an airlock (or partial airlock) in the heating coil inside your hot water cylinder. If so, the air may have entered the system when the pump was changed. There are two ways that I can think of to try and clear it. The first one involves finding the supply and return lines between the cylinder coil and the boiler. These should enter the cylinder on the same side, one directly above the other.
Having located the pipes, slowly slacken but do not remove the union where the higher one of them enters the cylinder. The head of water in the CH top-up tank should then push any air in the coil out in the same way as bleeding a radiator. If some air does come out, keep the union undone until only water comes out then re-tighten it.
The other method is slightly more awkward. Fit a hosepipe over the open end of the vent pipe that goes over the top of your CH top-up tank. This is the smaller of your two cold water storage tanks, probably in the loft. Attach the other end of the hose to a (preferably mains fed) cold water tap. Get an assistant to slowly open the tap whilst you look into the top of the tank. If there is air in the system, you will see bubbles coming up through the bottom of the tank. Once the bubbles stop, turn off the cold tap then remove the hose.
If the nearest cold tap is not mains fed, the second method will only work if the water level in the larger cold water storage tank is higher than that in the CH top-up tank. It will also take longer to clear the airlock than if mains fed. The tap on your kitchen sink should be mains fed, whilst those in the bathroom may not be. Mine are.
Please note that I am not a plumber, just a keen DIYer. Good luck. Oh, and one last point, make sure that the hot water and CH systems are turned off when you do the work to avoid getting scalded.