Differential Bypass Valve 1.1/4″

A differential bypass valve 1 1/4 inch is the larger size of automatic bypass valve. It goes on heating systems where flow changes a lot because zones or radiator valves keep opening and closing.

How a differential bypass valve 1 1/4 works

When enough of the system shuts down, the pressure difference between flow and return rises. The valve senses that and opens, so water can circulate back through the boiler. That helps stop the boiler cycling on and off for no reason, and it takes load off the pump. So it suits larger houses, flats served by a shared plant room and light commercial heating.

• Size: 1 1/4 inch
• Fitted between flow and return
• Only two joints to make
• Can go in any orientation
• For systems controlled by zone valves or TRVs

Because it can go in any position, you can tuck it in wherever the pipework allows. Use suitable adaptors to bring the 1 1/4 inch connections onto your pipe size. If the valve has an adjustable setting, set it with the system running and most zones closed, so it opens just as the pressure starts to climb.

Larger bypass valves from our Glasgow shop

Browse our heating controls for pumps and other valves.

The Plumb Parts counter at 555 South Street, Glasgow G14 0QX opens Mon-Fri 8am-5pm and Sat-Sun 8am-1pm. Online orders are taken as well.

Specification

• Sizes: 1 1/4″
• Suitable for: Larger heating systems controlled by zone valves or TRVs, fitted between flow and return

Common Questions

What does differential mean on a bypass valve?

It opens on the difference in pressure between flow and return, not on the pressure in the system as a whole. That is why it responds when zones close.

How do I connect a 1 1/4 inch valve to copper?

Use threaded adaptors to suit the 1 1/4″ valve ends and your pipe size. Seal the threads with PTFE or paste.

Is this size for domestic heating?

It is mostly used on bigger houses, shared plant rooms and light commercial systems. A normal house usually takes a smaller bypass instead.