expansion tank problem

[andymc]

with my hot water on (pump running) I get a constant flow of water up the expansion pipe and into the header tank even when the system is cool and first starts up, the flow is constant and strentgh depends on pump speed, also the header tank does not overflow, it seems to circulate around the system....this all stops if I have central heating on with hot water, can anyone help, I do not know how long this has been happening and have not changed anything in the system

 

[chrishutt]

Classic example of pumping over. The problem is that the system pressure at the point where the vent pipe connects (after pump) is higher and the pressure at the point where the cold feed connects (before pump) is lower.

Normally the vent pipe would extend above the level of the feed tank enough to overcome this excess pressure. For example if excess pressure in vent pipe was 0.2 metres head and the vent pipe extended above the tank water level by 0.4 metres, the water would not rise enough in the vent pipe to overflow.

You need to have the system pipework examined by someone who understands these things to suggest modifications. Possibly extending vent pipe higher, if head room available, or connecting cold feed to same point in pipework as vent pipe connection.

 

[Nige F]

Sounds like yet another incorrect pipework job . You need to ascertain how the cold feed,and vent pipes are in relation to the pump,and ideally post a line drawing. There are some top notch guys here ,but not many psychics Cold feed/vent should be on suction side of pump.

 

[ChrisR]

Have you fot RED rusty water in the tank? If so it would be wise to clean and flush and add inhibitor to the system once the pipework is sorted out.