Issues with commercial heating system

[mfgs]

I have got a problem with a commercial system. One zone is working fine, the other isn't. There are two vaillant boiler linked together through a low loss header and controlled by a VRC 630 control unit.

When the zone which is causing issues is turned on, the zone valve opens as per the attached picture but the pump doesn't run. I have no power to the pump at all. When both zones via the override feature on the control unit then both pumps run but one zone gets really hot and the other the rads get luke warm. The return is the hotter pipe as well on the zone which doesn't heat up properly.

So I have two questions as I didn't have the time to have a proper look when I was there yesterday. When the zone valve opens should it switch on the pump or would that be controlled by anything else?

Why would the return be hotter than the flow?

 

[Last Plumber]

I have got a problem with a commercial system. One zone is working fine, the other isn't. There are two vaillant boiler linked together through a low loss header and controlled by a VRC 630 control unit.

When the zone which is causing issues is turned on, the zone valve opens as per the attached picture but the pump doesn't run. I have no power to the pump at all. When both zones via the override feature on the control unit then both pumps run but one zone gets really hot and the other the rads get luke warm. The return is the hotter pipe as well on the zone which doesn't heat up properly.

So I have two questions as I didn't have the time to have a proper look when I was there yesterday. When the zone valve opens should it switch on the pump or would that be controlled by anything else?

Why would the return be hotter than the flow?


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As far as what turns the pumps on, that depends how it's wired.


I cannot see any NRV's ? reverse circulation caused by the lack of those maybe?

 

[mfgs]

What could possibly control the pump? I'm new to the commercial world and I am trying to get a better understanding of systems etc.

There aren't any non return valves. Could a weak pump on one zone cause it to reverse circulate easily?

 

[ShaunCorbs]

the vaillint controller you should see hk 1 (zone number) p (pump)

do you have voltage coming out?

 

[mfgs]

the vaillint controller you should see hk 1 (zone number) p (pump)

do you have voltage coming out?

The controller was definitely opening the valves above the pumps but when the valve on the zone which doesn't work was open I was getting no voltage to the pump. Does the controller send voltage to the pump? And not the valve when it opens like on a domestic set up?

 

[ShaunCorbs]

Yes it sends voltage to the pump and the valve doesn't have an orange wire just two

 

[Last Plumber]

Follow this link to the manual and the wiring diagram.
You're best to read through the info there and then compare it to what you have on-site.
It is really supposed to be wired so the 630 controls the pump and a mixer valve, for example but people can wire things bespoke too. I know I have.
Which two Vaillant Boilers are they and which other controls do you have in the zones?

 

[mfgs]

Ok thanks, I will have to allow a couple hours to go back there and have a proper look. There is no mixer valve that I could see. Just need to work out why the pump isn't coming on. The zone valve opened and the boiler fired but the pump for that zone only came on when both zones were on "override" on the programmer