Should hot water work when secondary return switched off?

[osmononame]

Good evening all,

 

Quick question about a secondary return pump - i have one in my house and my plan was to switch it off at night so that the hot water is not continually circulating at night. I have put it on a timer but what I am finding is that when it is switched off I don’t get any hot water! Maybe its a bit tepid but certainly not hot - as soon as I switch the pump back on I get the hot water returning! A couple of things to add if it might help diagnose:

 

1.Our first pump failed, and we ran the system with the pump disconnected (so turned off at the valves on both ends of the pump) and it worked fine and we got our hot water albeit having to wait 30/40 seconds for the hot water to reach us and

 

2. When the pump is switched off the brass fittings on both ends of the pump are COLD to touch - almost as if ice cold water has been running through them - could anything obvious be causing this?

 

Surely i should get hot water when the pump is switched off? What could be causing presumably cold water to be running through the pipes when the pump is switched off? 

 

p.s. After a bit of googling it seems that I need a non return valve between the pump and uvc - can't see one on the system so hopefully thats it but if anyone can corrobate that would put my mind at ease.
 

Edited November 30, 2021 by osmononame

[PeterW]

No NRV and a circuit plumbed badly and the “hot” water is being pulled from lower down the tank. My guess is the plumber piped the hot return into the bottom cold feed and not the return port on the cylinder. Without a non return valve all you will get is cold water. You’ll also be cooling the whole tank when the pump is running. 
 

photos will help

[osmononame]

Thanks Peter. The uvc is a OSO Super Coil - so preplumbed for secondary return / system boiler (which we have) and the secondary return looks to be where it should be per OSO manual (via the expansion relief valve). However even the manual says to install a NRV - I have ordered one now so will try that and and take things from there.

[osmononame]

Hi all, I thought i would update this thread as this saga with my hot water has continued to run and run (or run out as is normally the case)!

 

The installer came out and installed a NRV between the bronze pump and the tank - that solved the lack of hot water when the pump was switched off but I am still losing a whole lot of heat through the tank and it can go from full hot to room temperature overnight. the plumber was out a few times and couldn't see anything wrong and I have lived with it until last night when I wanted a bath and what do you know! No hot water despite us being out of the house all day!! I have the bronze pump on a smart plug and so its only on when motion is detected in the landing - so most of the time this pump is actually off and so i shouldn't be losing any heat through the secondary return.

 

I ended up checking the piping myself last night and on the SC300 manual for the secondary return should be connected via the expansion vessel connection and the combination valve but my secondary return seems to be plumbed into the balanced cold water connection. Could this be causing my issue? To my layman's eyes where the connection is supposed to go and where it does go on the combination valve are not miles apart but surely this can't be right? The plumber has said it doesn't make a different and OSO technical hasn't responded to me.

 

Can anyone chime in while i wait for OSO?