Pump query

[CaseyJones1]

Ideal Mexico RS60 boiler, with gravity hot water.
On C/H pump start-up, a surge of water goes up both the feed and expansion pipe into the header tank, and also up the safety vent pipe at the same time (but no water actually comes out of the vent). Around half a pint up each pipe every time the pump starts.
As the hot water system is not connected to the pump (the pipes are on the opposite side of the boiler from the C/H pipes) what could be the cause of this?
The feed and expansion pipe is connected to the gravity hot water return, the safety vent is connected to the hot water flow.
The C/H pump is on the return pipe, just before it re-enters the boiler.

I'm getting air (not hydrogen) building up in the C/H radiators, so could the pump be sucking air in by so-called 'microleaks' or could it be aeration due to oxygenated water re-entering the system?

A professional heating engineer says teeing the f&e and vent pipes and blocking the vent may cure the problem, but why? (He didn't say.....)

 

[Agile]

I dont know how you can know how much water is going up a copper pipe!

It sounds as if there is air in your system.

If there is air in the system then there might be a leak on the suction side of the pump or even anywhere in the system. This usually results from a bad layout.

Tony

 

[CaseyJones1]

1. Drain header tank then measure the quantity of water pushed up into it.

2. See how much water gets sucked up the vent pipe from a container, after the air has pushed out of the pipe.(Approximate, but give me an idea of how much.)

And your explanation for the water going up the pipes on pump start-up..............?

I know there's air in the system, that's what I said.
I did mention 'microleaks' too.............

 

[CaseyJones1]

No ideas anyone, then?