Speed ​​/ efficiency of the pump in a boiler?

[Jojo57]

I have a 20kw Pulsating Auer boiler (cast iron radiators, old house) with hot water production since December 2007, it works correctly but it has already stopped 2 or 3 times in hot water production and once in heating . The pump does not seem to be blocked but to run without pumping, I suppose because there is a large air bubble.

My heating engineer told me that it was "normal" for the pump to block (or rather turn without pumping) because there is air in the pipe, especially at the beginning.

The answer seems muddy because in my previous installation the pump had never blocked in almost 20 years and I had several times emptied the pipes, there is always air in the circuit, I never got to the remove completely. Your opinion ? Did you have this problem ? how to solve it? (the new pumps are horizontal, the old one was vertical).

Here is my main question (and econological!)
The (there is a pump for heating and one for the production of hot water) were set to speed 3 (maximum). I set these pumps to speed 2 and for more problem (but it may be a coincidence).

My second question is what is the impact of the speed of a pump on the efficiency of the installation? With cast iron radiators and an old house, is it better to pump water quickly to heat better or on the contrary to pump less quickly and leave the radiators which have a fairly high thermal inertia while taking the heat of the water?

In summary I consume less gas by going faster or slower?

Thank you in advance

[Chatham]

If the pump deactivates there is a chance that the diaphragm of the expansion tank is hs ... (the water level being considered to be sufficient, and the circuit having been purged with the upper radiators)
In principle, if the circulation speed is insufficient, it simply won't heat enough ... inevitably it eats less gas when the loaves are frozen inside ...

[Jojo57]

The vase is new, the correct pressure, the old installation but new boiler and pumps, on the other hand I have trouble purging, there is always air (no leakage) but it has always been like that before. ..

This heats enough in position 2 or 3 of the pump now difficult to know (to test) if it would heat more in 2 or 3 because it would be necessary to test over a fairly long period with the same outside temperature.

[loop]

Good evening Jojo

For your pump speed problem

I asked myself the same question about the advantage of increasing the speed of circulation of water in a central heating circuit
I don't have a "pro" answer to give, but simply:
Personally, I think that if the pipe section of the installation is correct, the pressure drop is reduced and speed 1 is enough to push the water to the most distant radiators
I would say that forcing the speed (to 3) is a sign of a high pressure drop, therefore under-dimensioning of the tube sections, in other words a bad remedy rather than a real solution
Theoretically, the speed of circulation of the water in the installation does not change the quantity of heat taken from the boiler (otherwise it would be enough to slow it down as much as possible to have a super-efficiency)
On the other hand, it must be remembered that if the return water is cold, it is because the heat exchange of the radiators is good (delta t important) but the heating body of the boiler will not appreciate in the long run (at cause of dew point)

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