DIY Doctor UK DIY Forums

Hi, I recently had a burst pipe and all the water was drained from the system. Once the new pipe was fitted and the system bled i find that i could get the central heating to work but the hot water failed to get hot. Water still comes out the taps but is stone cold.

I was recommended to change the controls as it cold have been an electrical fault however the problem stays the same, and controls work just as well as before.

I have a baxi bermuda back boiler which seems to be firing up fine with the hot water. My hot water cylinder tank is stone cold and so are the pipes around it.

When the hot water switch only is on, my radiators to several rooms are becoming hot.

Hi bigd,

This looks like you might have an airlock in the heating coil inside your hot water cylinder. As to why some of your radiators are getting hot when set to hot water only, I'm somewhat confused. If they are upstairs it could be that a gravity feed has been set up through the CH system since it can't work through the cylinder coil. Alternatively, if you have a motorised valve in the CH pipework it may not be closing fully.

Anyway back to the possible airlock in the cylinder heating coil, there are two possible ways to tackle this. First, find two pipes going into the side of the cylinder one above the other. Slowly loosen (do not remove) the union fixing the top one of these to the cylinder. The head of water in your CH top up tank should then push the air out followed by water.
The other way is to fix a hosepipe onto the vent pipe on top of the CH top-up tank (the smaller of your two cold water tanks probably in the loft) with the other end onto a mains water fed cold tap. Then get an assistant to slowly open the tap whilst you observe the top-up tank. If air bubbles come up through the bottom of the tank keep the tap running until they stop. Be careful not to open the tap too far or the tank may backfill faster than its overflow can cope. Finally, just for information, I'm no more of a plumber than you are, just a keen DIYer.

Methinks you have an airlock somewhere in the feed to the coil in the cylinder.

Cheers