Central heating wiring.

[dingodeano]

Hello men. I haven’t posted on here for a while but I wondered if any of the experts of central heating wiring could give me a heads up.
This is probably beyond mere DIY.
I’ve got to go out to look at a job involving a y plan.
Apparently there is an issue with wiring. But the information I have is not anything I’ve come across before. There is a three port valve one direction heat one water which goes to cylinder however there is a second two port valve between three port and cylinder. What is the purpose of this valve? Safety? Cheers. I have limited info as I’m not going out until Monday thx in advance

 

[DaveHerns]

You'd probably be better posting in Plumbing and Heating

 

[John D v2.0]

Hello men.

Clearly international women's Day passed you by completely.

To answer your question, it's possibly an unvented cylinder? In which case the second one is a safety measure to prevent the cylinder causing a danger by overheating.

 

[dingodeano]

That was my assumption because the valve would serve no purpose except a limit of delivery of water into tank. Haven’t come across this configuration.
Thanks men...and ....ladies and everyone in between (lucky for some) ....I will know more next week.