Secondary return cools cylinder within 2 hours All aspects of plumbing questions and answers, help, tips and information

[Ben Adams]

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

[stoneyboy]

Hi Ben Adams,
It’s essential that the flow and return pipes of the secondary circuit are well lagged otherwise heat losses will soon drag down the temperature of the water in the HWC.
Regards S

[Ben Adams]

Thanks S, appreciate the input. This looks like I'm then going to have to get some insulation and lag what I can in the loft area. The problem I have however is outside of the loft area everything is sealed up now. The pipes run down from the loft through voids that were created either side of chimney breasts running through the house. Does this mean even if I lag the pipes in the loft the secondary return will still likely be redundant (due to its heat loss). Non of the heating pipes in the house have been insulated either. I'm basically weighing up whether or not I will need to reopen up parts of the house to gain access to insulate the pipes, which would be quite costly as we've just finished decorating! I've included some pictures here if they are of any use: https://imgur.com/a/U5KNNmK Many thanks. Ben

[stoneyboy]

Hi Ben Adams,
Many thanks for responding and including pictures. Presumably your whole heating installation is a work-in-progress. If you are to reduce your heating costs all hot pipes outside your house heated envelope must be lagged - the ones on the loft floor could also have 270mm of loft insulation over them. You will also need to identify your secondary circuit pipes and lag all of them or you will never retain heat in the HW storage cylinder.
Regards S

[Ben Adams]

Hi Stoneyboy,
As much as it pains me to say it, this was the 'finished' job. So I'm likely going to have to get someone back to insulate where necessary now. By identifying and lagging all of the secondary circuit pipes, do you mean opening up the walls and pulling up floorboards throughout the house?
Many thanks
Ben

[stoneyboy]

Hi Ben Adams,
If you want your hot water to remain hot when the boiler is off, you will have very little choice. You could try lagging all pipes you can get at easily and then decide whether a full lag is worth the effort.
Regards S

[Ben Adams]

Hi Stoneyboy, I guess that makes sense. I'll try and get up there and lag what I can in the loft and see if that helps. I noticed today though that some of the pipes are really close together, so I won't be able to get very thick insulation for parts. There are a lot of clips up there too, do you know how I would insulate around/over the pipe clips? Thanks. Ben

[stoneyboy]

Hi Ben Adams,
You’ll be lucky if there is 20mm under the pipe.
Use 22 or 28mm wall split foam lagging and cut along the length of the lagging with a sharp knife (snap off blades are ideal) to reduce the depth to clear under the pipe and to clear sideways. Cut square holes out where there are clips using the same knife.
Don’t bother to lag cold pipes - rely on loft insulation to protect them.
Regards S