Automatic Bypass Valve 22mm

Fit an automatic bypass valve 22mm between the flow and return, and the boiler always has a path for water, even when most of the radiator valves have shut. On a system full of TRVs, that is what keeps it quiet and working properly.

Why an automatic bypass valve 22mm matters

As rooms warm up, thermostatic radiator valves close. The pump keeps pushing, so pressure builds and you get whistling valves and banging pipes. The bypass opens at that point and lets water flow back to the boiler. That also keeps the minimum flow many boilers need, which matters most on low water content boilers.

• Size: 22mm
• Fits across the flow and return, after the pump
• Opens on its own as system pressure rises
• Helps with noise on TRV systems

Put it somewhere you can get a hand to the head. Once the system is full and running, close all but one radiator and turn the setting until the noise stops and the boiler runs steady. Check the boiler maker’s instructions for any minimum flow they ask for, because some boilers have a bypass built in already.

Collecting a bypass valve in Glasgow

Pumps, valves and controls sit together in our heating controls section.

Collect one from the Plumb Parts counter at 555 South Street, Glasgow G14 0QX. Counter hours are Mon-Fri 8am-5pm and Sat-Sun 8am-1pm, or place an order on the website.

Specification

• Sizes: 22mm
• Suitable for: Wet central heating systems with TRVs or zone valves, fitted between flow and return

Common Questions

What is an automatic bypass valve?

It is a spring loaded valve piped between the heating flow and return. When most radiator valves have closed, it opens and gives the pump and boiler a path for water.

Do I need one with a modern combi?

Many combis have a bypass built in, so check the boiler instructions before adding one. Where the maker asks for an external bypass, fit it as they show.

Where should the 22mm bypass go?

Fit it after the pump, across the flow and return, before any zone valves. Leave the head where you can reach it to adjust the setting.