I have a combi boiler, with 2 heating zones, each operated by a room stat, and each with a 2 port valve. Should the boiler have a bypass fitted between the heating flow and return, so that if both the 2 port valves failed, and the boiler was in demand, for some reason, then the return hot water would ensure it stops heating up? Ta,
If the valves failed to open they would not switch on the boiler. They do this by having a microswitch which switches the boiler when the valve is nearly open. In most cases, combi boilers have an automatic bypass internally. You can check if yours is one of these by phoning the manufacturers helpline and quoting the model number off the ID plate. Most manufacturers are only too happy to respond to this type of question.
Many thanks for the quick response! I ask the question because I think one valve (Boss Therm) is sticking 'Open' so powers the boiler even though the room stat is 'Off'. Then I thought what if this happens when the valves are 'Closed'. But, like ya say, that won't happen because the boiler won't power up. As I am going to change the valves for Honeywell, I wondered whether to put in a bypass at the same time as it was drained down. No necessary now. Do Honeywell 2 port valves have the same couloured wiring and connections as Boss Therm BZV22 valves? So are are direct replacement? many thanks,
2 port valves are wired with a permanent feed , they are switched by the stat but can stick on and call for heat even when the stat is switched off and not calling, boiler and pump run , normally valves will be shut if motor failed but you cant guarantee it, a bypass is a good idea anyway to keep system temp high when trv's shut off each room