I have a radiant system I am working on in my basement that has 3 100ft loops of 1/2" PEX and is powered by a Grundfos Alpha 15-55SF/LC and it's hard to say for sure, but I think I'm only getting a total of 0.5gpm flow rate, with about 0.15gpm per loop. I've tried all of the settings on the pump, but the higher settings do no better than the lower ones. The pressure in the system is higher than the gauges read, so higher than 75psi. It is currently set-up as an open system. If I turn on hot water in the house, cold water flows through the system at about 3gpm total.
1. Do you think there is a problem with my pump?
2. Can you suggest any other possible problems?
3. I am considering switching to a heat exchanger system, which will allow me to lower the pressure. Do you think this will allow the pump to produce a higher flow rate?

Thanks for your help.
Mark

Who designed/installed your HR system and why are they not troubleshooting and correcting the issues? Is this a new system or a recent problem to an older system that previously worked well in the past? Do you have a schematic of the system?  High pressure could mean the pump is operating okay, but something is limiting the flow rate.  Did you change something in the system recently...like replace a check valve incorrectly or close some valve?  Again, a schematic would help folks better understand and troubleshoot this.

The absolute pressure in the system has basically no influence on the flow rate (with the taps closed). Look at the difference in pressures at various points in the system.

I don’t have any way to look at the pump performance curve right now. However, I think that pump can generate something like a maximum of 20 feet of head at 0 flow rate and a maximum of 20 GPM flow rate at 0 head. So maybe a maximum of 9 PSI differential pump pressure? If this is an open system as stated, the water pressure is typically between 40-60 PSI. So it isn’t obvious to me how the system pressure would exceed 75 PSI. Now if this was a closed system that didn’t have an expansion tank or relief valve…

did you remove the pressure reducer from the circuit?

Sailaway, he had to repost this question because his last thread turned into a pissing match, with every one ignoring the problem and arguing about open loop, and who was better than who.

Maybe this time someone can try and help

One of the reasons I do not design or install "open" systems is the relative complexity of mixing high pressure potable water with low pressure hydronic components. . Let's start with an appropriate heat exchanger with a low-pressure hydronic sub-system on the radiant heating side. From this point we can design a standard system with familiar components and nomenclature.

If you DIY you have to CYA.

a heat exchanger and lower pressure wont change the flow rate of his system or fix anything.

See my previous post

Oh yeah, thanks for the reminder Krom…that tends to happen whenever the subject of open system or DIY gets mentioned around here…

So again, did the PRV get removed as recommended, did you confirm that the pump and check valves got installed in correct directions, and are all the shut off valves open?

Your observation that cold water flows thru the HR system when you turn on the DHW in the house is a good indication of your problem! Your schematic shows the cold water supply connected to your HR system?