Vented indirect central heating system - drawing air, why?

[kf]

Can anyone help me?

Our central heating system loses water every day and we spend ten minutes or so every morning bleeding the top few radiators. We have double checked every pipe run for leaks: nothing.

We then noticed some water escaping from the header tank overflow. We therefore think that this is where the water is going. But how is air getting into the system. We're are completely puzzled.

Any advice would be greatly appreciated.

Kevin.

 

[cross thread]

new problem ? could be a restriction developing,pipework design pump speed to high

 

[kf]

Gordon,

Thank you for your prompt reply.

The problem started this summer after we replaced three of our eleven radiators. The central heating system had been trouble free for years.

Does this help? I guess this eliminates pipeword design as a cause and probably pump speed too (although I will find out how to adjust the speed and turn it down to see if it makes any difference).

Most probably, your suggestion that a restriction developing is the answer - draining down and refilling the system to install the new radiators may have moved sludge around etc.

What would be the best thing to do about this? Pour treatment into the header tank? Power flush? Replace cold feed tee?

Kevin.

 

[oph]

Could be a case of you cold feed and vent being incorrectly positioned, too much water in the header tank to start with , or/and the vent pipe not going high enough in the first place causing something called ' pump-over' which is very bad for open vented systems.
Pump could also be set to high.
Im afraid there isnt just one reason, it could well be the result of several minor things

 

[45yearsagasman]

View media item 39013
If you can identify this area on your system and test as described, it may be a start to finding your problem.
The configuration may differ but the principle is the same for all vented systems.