Replace Pressure Differential Bypass Valve?

FB

Our Buderus GB142 sends hot water to the radiators with a circulator pump and a zone pump via a Watts Radiant stainless steel manifold with zone valves. The Watts manifold had a Watts pressure differential bypass valve bridging from Supply to Return. With the bypass valve slightly open, the system has been running nicely for seven years. The bypass valve recently began leaking from under the adjustment knob. I took it apart and was disappointed to find the plastic knob was cracked and there is no provision for improving the seal around the stem. With the valve removed and the manifolds capped, the system works just fine. My concern is that the pumps run for five minutes after the zone valves close when the heating call ends. Buderus intends the five minute period to purge heat from the boiler. The boiler circulator can move water through the pipe loop in the manifold, but that hot water can't travel more than about four feet. With no bypass around the closed zone valves, is there any danger to the zone circulator as it pumps against water that can't move? If you think we need a bypass valve, I'd welcome suggestions for a better design than the original. Does it have to be spring loaded? Could I fabricate one using a partly open ball valve? Thanks in advance for your advice. FB

SWEI

Sounds like the "circulator pump" is a boiler circ and the "zone pump" is on the secondary circuit? If you could post some photos of the near-boiler piping, circulators, and zone valves we can probably see how it was piped.

Pressure differential bypass valves are going the way of the dodo thanks to ECM smart circulators. You may be able to change a couple of parts and significantly improve the efficiency and quietness of your heating system.

hot_rod

Usually the thermal actuators on the manifold take a few minutes to close off completely after the call for heat ends. Most "break" the end switch in them quickly but still take a few minutes for the valve to close 100%.

I'm not sure what brand actuator on that manifold, Watts has used a variety of actuators over the years.

The spec sheet may tell you the close off time period, or observe the operation.

Does the relay light go off a soon as the call for heat stops? Watch or feel the actuator to see how long before it closes 100%

Some brands of thermal actuators have pop up indicators that show you the position of the valve. That would help determine if or how long the circ could be dead-headed.

The PAB valve does serve another important function by shedding some pump energy as valves open and close. Without it you may get some high velocities when only one or two zones are calling.

Replace it if you can, or eliminate it and upgrade to one of the various delta P circs. A pump upgrade would also save some energy consumption.