Y Plan central heating gets hot on hot water demand

[MPGASANDPLUMBING]

Hi guys, just want to get some advise, basically new vaillant regular boiler has been fitted approx 5 yrs ago, i believe it was back boiler previously. The heating worked fine till now and for some reason central heating radiators started getting hot on hot water only demand. I`ve checked 3 port valve on hw demand, it`s not letting by to central heating, but radiators are getting hot, no bypass found, (see picture) it might be getting heat to rads from cylinder return pipe. How to solve this issue and what else could cause this change of circulation direction?

 

[John.g]

If you have "checked 3 port valve on hw demand, it`s not letting by to central heating", then the pipe from port A on the valve is cold and there should be a immediate still resistance when you pull on the manual valve lever?

 

[Lou]

Hello I just wondered if you have resolved the issue? If so, if you could let us know how that would be great for any future queries on the same thing.

Many Thanks

 

[Last Plumber]

Sometimes the connection point of the cylinder return can cause this issue. I would have thought you'd notice that before today to be honest but not always. Has something changed?
Does your pump need to be on speed 3?