DIY Doctor UK DIY Forums

I have a good one which I wonder if anyone can help with?

Our central heating system is powered by a baxi boler which we have had serviced a number of time and which appears to be working fine. The problem however is that about 6 months ago you could hear the water running through the system - like trickles - which got progressively louder. To 'rectify' this (rightly or wrongly), I topped up the small tank in the loft (which apparently has something to do with the heating system) so that a pipe which hangs above the tank was immersed in the tank - I did this as I assumed that air was getting in to the system via this pipe and assumed that there shouldnt be an open ended pipe anywhere in the system. Having then released the trapped air from the radiators it definately appeared to cure the problem. However then a month ago a radiator started leaking - a small pinhole appeared near the top. I fixed this with some diy putty specifically for the job. Then 2 weeks ago, a pipe next to the hot water cylinder sprung a number of pin hole leaks. We got the emergency plumber out who replaced the pipe but he was only a young lad and by his own admission wasnt a heating expert. He said that the pipe was hot and shouldnt have been and that there was something wrong with the heating that probably caused it. He also said there was a problem with a device that is attached to the pipes which lies next to the cylinder and which he says controls the hot water and the central heating. (this looks like a small square box with a switch underneath it) He also emptied water from the small tank so that the pipe that I immersed is now open again and as a result the gurgling has restarted. I have also noticed that the small tank is full of dirty water - not clean - surely this isnt right? And to top it all the fuse in the heating clock has blown twice in the last 6 months. And just while Im at it the water is constantly hot no matter what temperature the boiler is set at. Any ideas anyone?

Pinholes in a heating system particularly the pipes is always a ominous sign. The cause needs to be found and rectified immediately to prevent irreversible damage to your enitre heating system.

Quick chemistry lesson. Fresh water contains oxygen which corrodes metals. This is why heating systems are designed as a closed circuit, so oxygen cannot enter and damage heating systems.

Your system sounds to be badly designed which is allowing air to be drawn in via the expansion pipe into the closed circuit. It is no answer to cover the vent pipe, as that is only stopping the audible problem. The header tank water containing oxygen is still being circulated around the system.

Turning the pump setting down may avoid air being drawn in, but may cause some rads not to heat.

The best thing is to get someone in who can rectify the problem before the system fails again.

Thanks for the reply Martin. Ive spent the best part of day completely draining the whole central heating system. I was amazed at just how dirty the water was - almost black and plenty of sludge. When replacing the system I poured some sludge remover (cant remember what it was called but bought it from b&q and its supposed to aid eliminating sludge and dirt). Im planning on performing the whole operation again in about 3 4 weeks time in an attempt to completely clear the system and to also put in fernox. Weve been in the house for over 10 years now and this has never been performed so I guess it just built up over the years - when your no expert and the system works fine you have no idea that these things need performing. I am concerned however as to just how much damage may already have been done, but guess I will have to wait and see. Im definately going to take your advice though and am going to try and find someone that comes recommended to check it out for me, as Im suspicious of a lot of folk who may give bad advice and who may suggest changing things that dont need changing, etc. The whole system is certainly a lot quieter since the change and also the water isnt as hot, which does give me some faith that ive done the right thing. I have also ensured the overhang pipe isnt submerged having learnt that that it shouldnt be and that this is simply an overflow for the system - and still there is no gurgling - surely a good sign. I'll post an update in a few weeks time, to let everyone know how Ive got on, so that it can help others who may experience similair problems.

If the heating filler pipe from the header tank enters the circuit at a different place to the expansion pipe, particularly if they are on either side of the pump, air can be sucked into the system, or in the opposite case, there can be a constant trickle of water out of the expansion.

If this imbalance is confirmed, have someone re-position either expansion or feed pipe so there is no opportunity for a pressure differential between the two to occur. Put the expansion on the highest part of the system, and the feed a foot or two lower in the same pipe. Consider when redesigning, that the expansion must allow for steam to escape if the water was ever to boil.

Obviously a system full of sludge will slow the circulation and exacerbate the situation.

Don't leave the sludge remover in for longer than the manufacturers istructions as it is corrosive, and itself will in the long term cause damage.