Myson Automatic Bypass Valve 22mm

An automatic bypass valve 22mm is fitted between the flow and return pipes near the boiler. When the thermostatic radiator valves close down, it opens to let water circulate so the boiler always has some flow through it.

Why fit an automatic bypass valve 22mm

With every TRV shut, the pump pushes against closed valves. That makes the system noisy and can starve the boiler of the flow it needs. The bypass valve opens as the pressure rises and keeps water moving, so you no longer need to leave a radiator without a TRV just to act as a bypass.

Many boiler makers ask for a bypass in their instructions, so check the manual for where it should go. Fit it the right way round by following the flow arrow on the body. Where the 22mm valve can be adjusted, choose a setting that keeps it closed with the rads open but lets it open as the TRVs shut.

After commissioning, close the TRVs one by one and listen for noise.

Other heating parts are on the site in the Flexible range.

Bypass valves in Glasgow

Plumb Parts, 555 South Street, Glasgow G14 0QX: counter opens Mon-Fri 8am-5pm and Sat-Sun 8am-1pm. Online is available too.

Specification

• Sizes: 22mm
• Suitable for: Keeping a minimum flow through the boiler when TRVs close

Common Questions

What does an automatic bypass valve do?

As the TRVs close, pressure builds in the system. The bypass opens and lets water flow from flow to return, so the boiler keeps a minimum flow and the pump is not pushing against shut valves.

Do I need one with a combi boiler?

Many modern boilers have a bypass built in, but not all. Check the boiler installation manual, which states whether an external bypass is needed and where it goes.

How is it set?

Set it so it stays shut with all the radiators open, and opens as the TRVs close down. Follow the flow arrow on the body when fitting it.