Secondary return cools cylinder within 2 hours

[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

 

[ShaunCorbs]

Sorry to say it needs super insulating yes also there should be a stat connected to the pump so once upto temp it turns the pump off so not pumping all the time

 

[Timmy D]

Needs insulating and could add a timer to secondary return to come on during peak times.

 

[SimonG]

What size pipework has your hot pipework and secondary return been ran in?

 

[Ric2013]

Also wondering how long your cylinder stays warm if you don't use it at all. I actually only heat mine 3 times a week, (which may not be best practice, but the point is that it remains warm at all times, unless we actually use a lot of hot water and so run it out). There are a few ways that a poor cylinder insulation can lead to heat loss, even when the cylinder is well lagged.

Looking forward to the pictures. Happy to help advise if I can as I always like the idea of cutting fuel bills. Insulation is possibly the least sexy energy-saving technology, but it is nearly always a very good idea. Not always entirely as cheap as we might like, but the savings go on and on and it doesn't really tend to wear out.

 

[Ben Adams]

Hi all,

Thank you so much for you responses. Okay, so it appears I'm going to have to get some insulation then and insulate where best I can. I will only be able to insulate the pipes in the loft as everything is closed up elsewhere now, the pipe work basically runs down from the loft through cavities either side of the chimney breasts throughout the house. Here is a link to some pictures, if that helps to shed some light on the situation! https://*********/a/U5KNNmK Would be good to get an idea of whether the setup seems logical at least (regardless of the lack of insulation), as I naturally have concerns now that it could be a negligent job!

Once again, many thanks for your input.

Ben

 

[Ben Adams]

Also wondering how long your cylinder stays warm if you don't use it at all. I actually only heat mine 3 times a week, (which may not be best practice, but the point is that it remains warm at all times, unless we actually use a lot of hot water and so run it out). There are a few ways that a poor cylinder insulation can lead to heat loss, even when the cylinder is well lagged.

Looking forward to the pictures. Happy to help advise if I can as I always like the idea of cutting fuel bills. Insulation is possibly the least sexy energy-saving technology, but it is nearly always a very good idea. Not always entirely as cheap as we might like, but the savings go on and on and it doesn't really tend to wear out.

Hi Ric, the cylinder will stay warm for maybe 12 hours max if we don't use hot water. I generally heat the cylinder for 1.5 hours in the morning and by late evening it would be cold even if we used no hot water. If we have a couple of showers in the morning it is usually cold maybe 6 hours after being fully heated. This is all with out the secondary return pump on, if the pump is on then we lose hot water within 2 hours.

Thanks, Ben

 

[Ben Adams]

Hi all,

Thank you so much for you responses. Okay, so it appears I'm going to have to get some insulation then and insulate where best I can. I will only be able to insulate the pipes in the loft as everything is closed up elsewhere now, the pipe work basically runs down from the loft through cavities either side of the chimney breasts throughout the house. Here is a link to some pictures, if that helps to shed some light on the situation! https://*********/a/U5KNNmK Would be good to get an idea of whether the setup seems logical at least (regardless of the lack of insulation), as I naturally have concerns now that it could be a negligent job!

Once again, many thanks for your input.

Ben

Hi the link above was imgur dot com for the starred out section if that works?

 

[Scott_D]

How many litres is the cylinder

 

[Ben Adams]

How many litres is the cylinder

Hi Scott, the cylinder is a 250l horizontal everflo. I did try and post pictures but not sure they allow the posting of a url on here.

Steve

 

[oz-plumber]

I would hazard a guess that there is something else going on when the secondary return pump is on.
I doubt you would lose the heat from the cylinder and pipe work in that amount of time, if you haven't used any hot water.

Is there a pressure relief valve on the secondary circuit that may be passing when the pump is running?
This would cause an influx of cold water to the system - when the pump is running.

Sounds odd, but even un-insulated pipework, should not lose that much heat over that time.

 

[Peterdevon]

I had the same problem, the pipework under the ground floor was uninsulated and would cool the cylinder in about 2 hours, I have now got 19mm lagging on all the pipe work but it will still go cold if the pump is left running all day.

 

[Ben Adams]

What size pipework has your hot pipework and secondary return been ran in?

Hi Simon, thanks for the response. I've just been up in the loft and it looks like the hot pipework has all been run in 22mm pipe with the secondary return in 15mm. Thanks. Steve

 

[Ben Adams]

I had the same problem, the pipework under the ground floor was uninsulated and would cool the cylinder in about 2 hours, I have now got 19mm lagging on all the pipe work but it will still go cold if the pump is left running all day.

Thank Peter, that's interesting to know. Hopefully insulating the pipework in the loft will help! Thanks

 

[Ric2013]

Well, I'm thinking if your HOT OUT goes in a roughly upwards direction from the cylinder, you may be getting one-pipe circulation within that pipe even when pumps are off and no one is drawing water. From the photos, I'm having a hard time visualising which way is up and what connects to what, but if you follow the pipes with your hands, you'll soon get the idea which pipes are getting hot (losing lots of heat!), and which pipes are merely getting warm.

Last time I looked, Toolstation had some pretty good prices on what they call 'byelaw' insulation. It's only 1m lengths, but if you evostik all along the split and joints, it should work well.