myson boiler help

[toptinker]

hi, i have a myson boiler approx 18 years old. has worked fine all this time, had a few spares thermocouples, thermostat 2 x controllers and 3 way motorized valve. i have just fitted a new 3 way valve (actuator only) and noticed a 15 mm dia copper pipe with a shut off valve. this pipe is between the pump and 3 way valve not sure what this is for but also should the shut off valve be fully open or closed (is it to refill the system ?) the system is an open vented sytem but i cant see where the pipe goes to

 

[gasandoilman]

have you a photo??

 

[baxpoti]

By pass valve?

 

[toptinker]

could be, i seam to remember years ago before i did any work on the system that the valve was closed. if i do close it will that cause a problem.having tried to have a closer look it does look like it goes to the water mains ? (so a constant feed )also what if the valve is kept open ?

 

[twgas]

if your system is working, leaving valve alone would probably be the best bet

 

[toptinker]

yes boiler now works ok. when the hot water is on its fairly quiet.when the central heating is on after about half an hour it does a lot of banging and rushing water sounds from the boiler then tales off and on. i have opened the by pass valve a touch more to see how it went seams about the same what do u think ?

 

[Soggy_weetabix]

If you have a 3 port motorised valve, leave it shut.

Dave