There's a limit on how fast you can move water through a system for long-term reliability...too fast and it starts to make noise, could cause cavitation, and that can cause literal wear on the insides of the systems...wearing away the metal. Are there any valves in the system? If you have any partially closed, at restriction could cause imbalances. How many feet is it from the boiler location to the highest point? Are you sure you got all of the air out of the system? What pressure are you running? You need enough to ensure there is some pressure at the highest point...water column pressure will drop about 0.43#/foot of elevation change. Your pump needs to be able to overcome the head pressure, but the falling water on the return means it will flow if you can get it over the top...any air there will potentially stop it. Last, depending on the type of radiator...they could be quite corroded internally, and no amount of pressure will flow much through them. Same is possibly true if the pipes are iron and there has been any leaks...adding water means adding dissolved oxygen, which means rust, which means restrictions.
Your answer (as well as Tom's) seems to show a lot of experience (and received a like).
What do you mean "
What pressure are you running"?
-We are using 3/4 Pex (barrier) and new space saver radiators. It is possible that the pex fittings (which are smaller (1/2 inch)) along with all the twists and turns in the radiators contributed to the problem.
-The boiler kept on reaching high limit and shutting off
(on each of the three zones including the basement
). This happened only by the
radiator heat, but did not happen when heating the water in the tankless water heater (which uses 1 inch copper)- so there is no problem with the boiler. The original licensed professional boiler specialist gave up on hope the non working system and blamed the ones who installed the radiators.
-The water is moving tooooo slow even with 2 pumps. I tried almost everything you said. Bleeding etc. The returning water was heating extremely slow. Finally adding a second pump to each zone helped a little. In addition we lowered the setting of the boiler and a few other things. This helps But still causes occasional boiler shutuff.
- Now I just added additional house space to be heated and more radiators to one zone and the two pumps are again not enough.
A-Based on your response There are still two things for me to try -
1- See if the check-valvles are adding too much restriction
2- Take a closer look at the flow rate of each zone - if one zone does better than others I will try to identify the cause.
B- Back to my non conventional idea of adding more pumps:
To make things even more complicated for a non experienced plumber: If 2 or more zones turn on together at once - the boiler does not overheat. This is probably because we have more water and pumps coming in.
This is why I want to know if I put 3 pumps on the main supply line and then just 1 pump on each zone, will the pump on each zone direct all the water from the previous 3 pumps to only go into it's zone and not the other zones?
