Do I need a external bypass if my boiler has one? Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[greg555]

Hi,

Can anyone help??

My radiators used to only get warm on top. A plumber eventually diagnosed the problem as
being the external bypass in my heating system being fully open causing alot of the hot water to go directly back to the boiler. He closed the bypass fully and now the heating is 10x better

My questions are... should he have fully closed this bypass off? Is there no in between Fully open or fully closed? If the boiler has an inbuilt bypass what should the external one be set at? Will it damage my system etc if its fully closed?...

Any help would be VV much appretiated !!

[htg engineer]

You only need an external bypass if, your boiler does not have an internal one and:

a) you have thermostatic radiator valves fitted to every radiator
b) you do or your intention is to turn off every radiator.

If you want to leave the bypass closed as a precaution - fit lockshiled valves to both ends of one radiator. then this radiator cannot be turned off accidentally.

[greg555]

hi thankyou V much for your reply!

Can I just clarify this.. My boiler has a internal bypass so is it ok for the external one to be fully closed?

If a bolier has an internal bypass is the external one always closed of as as a default setting?

I mean when a plumber fitts a boiler and he/she knows that it has an internal bypass will they close of the external one, or is it a matter of preference?



Thanks again,
Greg.

[htg engineer]

If there's an internal bypass there's no need for an external one - it may be a case of the pipework is off the last boiler maybe ? maybe the last boiler didn't have an internal bypass.

Yes it will be fine left closed. - like I said as a precaution you could add lockshield valves to both ends of one radiator - then this is the bypass.

[greg555]

thankyou!!

One more small question (i promise)

I moved into a new build, so I guess they put the external bypass there if I wanted to change the boiler (without an internal bypass).

Q should the external bypass been left fully open in your opinion when I moved it? Or should the builders have closed it off because the boiler has one?



Thanks again,
Greg.

[htg engineer]

As long as your boiler has an internal bypass then leave it closed - otherwise it can cause problems as you have found, when left open the water could return at the same temperature as the flow, the system will not work effectively or efficiently.