twin cylinder setup

[Jimbob]

hi, i looked at a twin vented cylinder fully pumped setup yesterday which has had some problems which need rectifying. Its uses a Y plan setup.

First of all, is that when just 'hotwater' is on, the heating starts to warm up. So im fairly sure this just needs a swept tee where the heating joins the return back to the boiler.

The other problem is that it has a 3 port mid-postion valve which then just tee's off to each cylinder. Now the problem being is that the cylinder stat is only on one cylinder, And its the cylinder with the longer pipe run (flow) to it. So it seems the other cylinder is warming up alot quicker and therefore boiling up. So im thinking i could either, transfer the cylinder stat onto the 'prefered' cylinder. Or i could fit valves to each cylinder return and attempt to balance the flow through each. Or could get rid of the 3 port valve, And fit 3x 2port valves, one to the heating, and one to each cylinder, each being controlled by seperate cylinder stat's.

Advice most welcome.
Thanks, Jim

 

[doitmyself]

First of all, is that when just 'hotwater' is on, the heating starts to warm up. So im fairly sure this just needs a swept tee where the heating joins the return back to the boiler.

Reverse circulation. Check that the return from the HW cylinders comes after any radiator returns.

The other problem is that it has a 3 port mid-postion valve which then just tee's off to each cylinder.

I presume both cylinders are on the B branch and CH on the A branch.

Now the problem being is that the cylinder stat is only on one cylinder, And its the cylinder with the longer pipe run (flow) to it. So it seems the other cylinder is warming up alot quicker and therefore boiling up.

Are the cylinders identical, or is one fast recovery?

So im thinking i could either, transfer the cylinder stat onto the 'prefered' cylinder. Or i could fit valves to each cylinder return and attempt to balance the flow through each.

Transfering the stat will stop the "hot" cylinder overheating but the other one will now be colder than required. You should still balance the flow, even if you put in extra zone valves.

Or could get rid of the 3 port valve, And fit 3x 2port valves, one to the heating, and one to each cylinder, each being controlled by seperate cylinder stat's.

No need to get rid of the three port. Just add a 2-port into the flow to each HW cylinder with a separate stat on each cylinder. The HW stat will control the valve opening (brown and blue). Grey to permanet live, Orange to boiler ON (i.e as existing HW stat call wire). The HW stats are in parallel, so either can call for HW to be heated.

 

[Jimbob]

ok, well that explains some things. The return is indeed in the wrong place. No need to make an injector tee then?

valve is correctly piped. Cylinders look identical, theres 2 because of the lack of height. Dont really understand how you can balance the cylinders, using a thermometer on both returns i presume?

Not sure on the wiring side, sounds tricky wiring in a 3 port with 2x 2port valves. But im sure electrican will be able to handle it.

Thanks for that, great answer.

Just one more question, there is also a secondary return on the system, and they seemed to have connected it into the cold feed, is this correct, because iv never seen it done like this.

thanks again, Jim

 

[migoplumber]

each cylinder requires its own stat. the instalation sounds squiffy at best. your idea of the 2 port valves is good, make sure to use spring loaded controlled by cylinder stat, and you will need a bypass or shunted header, depending on your boiler set up

 

[justlead1]

Hi If secondary return is into cold feed it is possible to completely drain the cylinder via taps in some instances.

 

[Jimbob]

seems the guys who installed it couldnt of got it anymore wrong. They had header tanks put in (massive ones) which required a structual engineer and lots of steel girders, when they could of just had unvented cylinders. Also they have just linked the secondary return to a switch, So if you want that to be timed, would it require some kind of relay?
thankyou very much. great help
Jim

 

[doitmyself]

Dont really understand how you can balance the cylinders, using a thermometer on both returns i presume?

Same as balancing a radiator. When the valve is in mid position, you don't want the cylinders getting all the flow

Not sure on the wiring side, sounds tricky wiring in a 3 port with 2x 2port valves. But im sure electrican will be able to handle it.

On a Y Plan the mid position valve does nothing in HW or HW & CH; the boiler is controlled by the cylinder thermostat. We are just replacing the cylinder thermostat by two stats controlling motorized valves with auxiliary switches, which supply the voltage to the boiler.

Just one more question, there is also a secondary return on the system, and they seemed to have connected it into the cold feed, is this correct, because iv never seen it done like this.

According to Treloar, a secondary return should be fed into the top third of the cylinder. Feeding into the bottom of the cylinder, e.g cold fill, reduces the waer temperature.

As Migo says, you will need a bypass or shunted header, even if you retain the 3 port valve. This is because there will not always be an open path.

 

[david williams]

anyone can call themselves a plumber and heating engineer,but it seems very few have the training and expertise to carry out the work corectly.proper ongoing training and legislation is the only way forward.

 

[Jimbob]

This job is at a mates place. And he got me in too look at it, but its been 4 years since it was installed. And most of the problems started from day one. And the plumber had been paid and had no intrest in coming back. Been there for half a day today, thought i had combatted most of the problems, But after digging about, i have found more.

there is a secondary heating loop which returns in between the cylinder and boiler room, this loop doesnt seem to have a 2port valve and seems to be just controlled by the pump. This is lightly to be the problem. But without massive work its going to be inpossible to make the cylinders to return in last.
So do they make a high flow single check valve which will stop the reverse circulation?

Also for some reason the cold feed from CWSV seems to be getting hot, and its even heating the cold water. Think this is down to the hot return connecting into it. But this is slighly concerning. A complete nightmare to try and figure out how the system has been pipes, as it is oak floors and tiles everywhere.

Cheers, Jim

today a revalation. I have found that the 2 cylinders are somehow self circulating. Hence why one is heating up the cold feed. It seems to stop doing it when you shut the supply to the other tank. Strange seeing at the tank connections are at near enough the same height.

Has me scratching my head even more now. Any ideas on this one? We was thinking that cross linking the cold feeds may balance them.

 

[Jimbob]

bumpey bump bump, nobody have any idea with this?