Primary Secondary Flow Direction

OLmako20

Good afternoon, great resources on this site!

I am a homeowner/DIY and had an installation of a Vitodens 100 B1KA w/on demand DHW a few years ago. The installed didn't go that well as the contractor hooked the boiler up in reverse. This was very noticeable as DHW had uncontrolled temperature as it was flowing in reverse so the outlet temperature sensor always thought it was cold because cold water was flowing in. They corrected that and the DHW temp was resolved.

The boiler has been in service for a couple of years and working OK however I noticed that the primary and secondary loops are also reversed. As I stated the house has been heating OK, but I am sure the boiler is not operating at its peak efficiency. Basically the boiler gets pre-warmed water as it mixes at the closely spaced Ts with the return water from the radiators. I know there is mixing here based on the demand of the system, but I would think this would really raise the return temperatures to the boiler unnecessarily.

The fix would be to re-plumb, which I plan to do at some point, but would switching the direction of the secondary loop circulator work? this is a quick unbolt flip over and re-bolt. This would mean the zone valves and pump are on the return side, not sure if there is any issues with that.

Below is the schematic of how the system currently is plumbed.

Thoughts?

EdTheHeaterMan

That will work only if you also reverse the zone valves. If you look closely at the zone valves there is an inlet and outlet. When the zone valve is installed backwards, you can get other problems.

another point is that the hottest water will go the what used to be the coldest part of the system. That may or may not be a problem, depending on how the system is designed.

hot_rod

Most zone valves are directional, they will have flow arrows on them. Reverse flow will often cause them to bang or hammer.

Reversing at the tees may be the easiest, best fix.

EBEBRATT-Ed

Its piped wrong the supply and return at the two closely spaced tees need to be swapped.

I don't get what the zone valves have to do with this. If you reverse the zone pump you would have to reverse the zone valves. That is more work than swapping the two pipes.

OLmako20

Thanks for the feedback. Yes I agree probably just best to swap the Ts. Now my next question, do I need to swap the spriovent? And water makeup to the supply side of the primary loop? Since i will be opening up the system anyway is a low loss header worth the extra effort/money over closely spaced Ts?

hot_rod

Is the spirovent on the hot supply out of the boiler? If so it looks like the tees are correct.

OLmako20

no it’s on return side

EdTheHeaterMan

I just answered a question with a Similar problem where the return and the supply was reversed. His was trying to solve a different problem but offered the diagram in this post.

https://forum.heatinghelp.com/discussion/comment/1837653#Comment_1837653

Here is the diagram as his system is installed. See the closely spaced tees and how they are reversed. I don't believe that he knows that reversing the supply and return like this is a problem. All he wanted is to solve is the noise issue.

First Diagram reposted here

Take a look at the second diagram and see how easy it would be to make yours look like that one. Disregard the DHW loop if you are not using an Indirect Water Heater.

Second Diagram reposted here

I offered the second diagram to resolve his noise problem and to correct the reversed piping on the closely spaced tees. See if your system can be repiped this way where the Expansion tank is located on the boiler loop supply side I understand that your boiler pump is internal to the boiler unlike this diagram, but all the parts are in the right order for noise free and trouble free operation

OLmako20

thanks for the advice. I think once the winter heating season is over I’ll take a crack at repiping the system.

Is a hydraulic separator vs closely spaced Ts a good improvement, like the caleffi hydrosep? It would be more of a project, but since the system will be open anyway might be a good time to.

PC7060

simplest thing is to swap the connections at the boiler, leave T as is, and see how it performs for a year. With exception of the input/output piping mistake at boiler, the installed did nice job. You’ve got isolation valves in the secondary loop so won’t have to drain down system.

hot_rod

it becomes a little weird when you have two expansion tanks in a system. Two PONPC locations

Your boiler has a pancake expansion, and you have added a second. The one in the boiler, probably a liters, size may be close in capacity to a #30 an be adequate on its own? You would need to know or guesstimate the water volume of the system

Those metric tanks have a small BSP thread, so it not easy to adapt a larger external tank into that connection point.

Some mod cons have high head circs, that one may as it looks to be a coil type boiler HX. the correct expansion tank connection can be more critical, so you don’t pop relief valves with the added delta p.

PC7060

@hot_rod - is the expansion tank the vertical rectangular object at upper left of boiler?

hot_rod

https://forum.heatinghelp.com/discussion/comment/1837748#Comment_1837748

yes

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