Grundfos 26-64 pump opening Honeywell zone valve.

Alan (California Radiant) Forbes

I have a customer who says that his master bedroom zone overheats. The room continues to heat when the thermostat and zone valve are off and one of the other zones is on. The Honeywell zone valve operator was replaced by another contractor which didn't help and I almost replaced the valve today until I decided to check his system pump which is a Grundfos 26-64 which I believe is oversized and could be forcing the zone valve to slightly open, heating the space. This overheating happens only in the master bedroom zone which is furthest away from the pump. If I manually open and close the zone valve at the lever on the operator, it feels fine.

At this point, I don't know whether to replace the pump or the zone valve.

Honeywell spec's.: https://forwardthinking.honeywellhome.com/related_links/water/5000_series/install/95c_10932.pdf

Grundfos spec's:
https://product-selection.grundfos.com/product-detail.product-detail.html?custid=GMA&lang=USA&productnumber=52722330&qcid=471285683

Flowing 8 gpm @ 6' head.

NY_Rob

I had one of those Honeywell zone valves with the rubber ball plug that closes the valve off. On mine the ball had deteriorated to the point where there wasn't much of it left and it was doing nothing to stop the flow of water past it even when closed.

SuperTech

Have you ruled out gravity flow? Are the zone valves on the supply or return? Do you have any pictures of the piping?

Zman

You might need both. I agree that the pump is oversized. Has it trashed the valve?

hot_rod

that is a very low shutoff pressure on the high Cv valve? Typically a 20 psi shutoff for large Cv, up to 75 psi on smaller Cv valves. No doubt even a 15-58 could push open that valve.