Secondary return cools cylinder within 2 hours

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Ben Adams

New Member
Jan 16, 2023
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I'm a plumbing novice so first of all I apologise if I'm not explaining this situation correctly. I've recently renovated a house for my family to live in and we're having an issue with water not staying hot when the secondary return circuit is on. From a starting point of fully heated the cylinder is usually cold again within two hours of running the secondary return. When the secondary return pump is switched off the water will stay hot in the cylinder for maybe 8 hours, depending on usage. The plumber who installed the system (who has now left the job and won't return) never insulated a single pipe on the secondary return, in fact he didn't lag a single pipe in the entire house (hot water and heating). Is it possible the secondary return could cool the cylinder that quickly due to heat loss through the pipes? The boiler and cylinder are fitted in an uninsulated loft and so there is exposed pipe work up there before the pipes feed down one floor into the main envelope of the house. I've done some searching on the internet and it looks like most pipes around the cylinder and boiler are usually insulated and so I'm wondering if I should get up there and start lagging the pipe work myself, as my bills are excruciating at the moment. One other potential cause a friend suggested was that there may be issues with how a non-return valve is set up, and so cold water could be unintentionally entering the cylinder as a result. I'm really at a loss, so any suggestions would be much appreciated. I can post pictures of the setup if necessary! Thanks
Just wondering if anyone had any suggestions now there are pics to shed some light. Thanks. Ben

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