Normally open 2 port valve with open therm boiler

[PCA]

Firstly can you have this type of valve on an invented hot water cylinder?

Secondly what will it achieve in having it as I cannot see what improvement it will make

Any advice would be cool

Cheers

Paul

[Richard]

A normally open (NO) valve is for the heating side of the system when using OpenTherm, not the hot water side. You would still have to use a NC valve for the hot water side...

[billytkid]

I just installed my system like this, this week.

Have NO valve on CH system, NC on DHW loop. Then have BDR91 as DHW control.

When DHW time starts, it turns off CH and all heat from the boiler goes to DHW.

I am going to put a manual switch between the BDR91 and NO valve though, because this setup means CH always turns off when DHW is needed - and in the depths of winter this may mean the house temp dropping while DHW is on. In this case I'll disable the NO valve, so both CH and DHW will pull at the same time

[Richard]

I am going to put a manual switch between the BDR91 and NO valve though, because this setup means CH always turns off when DHW is needed - and in the depths of winter this may mean the house temp dropping while DHW is on. In this case I'll disable the NO valve, so both CH and DHW will pull at the same time

This is no different to combi boiler? Hot water priority means the cylinder has a very fast recovery... I Don't know any installer that does this on PDHW?