Help! Pressure keeps rising on Weil McClain Eco 70 system

ChrisCS

I'm hoping someone can help me figure out what the problem is with my home's hydronic heating system. I have a Weil McClain Eco 70, installed about 9 years ago. The system is great, but recently had the system serviced and the expansion tank was replaced. I don't have an auto-fill valve - it is a manual fill valve. The pressure, when not running, was about 18 PSI or so. Now, ever time I run the system, it spikes to about 25 PSI (which is OK, I suppose), but then the cold/not-running pressure is slowly increasing… I'm now up to around 21 PSI when the system isn't running. Any ideas what the problem could be? Was the expansion tank installed wrong?

Jamie Hall

Two different problems.

The slow rise in cold pressure can only come from the manual fill valve leaking by — very slightly, but leaking nonetheless. There is no other source of water to increase the pressure. You might get lucky and persuade it to stop by lowering the system pressure and then turning it full open and firmly closed… but it may need replacing.

The excess rise in pressure when the system goes from cold to hot is likely due to the expansion tank not being properly charged with air when it was installed. There is only one way to do this right. Disconnect the tank from the system (if you have the right combination of valves and drains this is easy. Otherwise, you will have to drain the system and disconnect the tank. Charge the tank with air to the desired system pressure. Then reconnect the tank to the system and set the system pressure.

ChrisCS

Thanks, these are two good suggestions! Is charging the expansion tank a job that I can handle on my own (with some YouTube tutorials, no doubt), or is it something I really should call a professional for?

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1856273#Comment_1856273

Charging the expansion tank isn't rocket science — but how easy it is to do depends on there you have valves. It can be very easy — if there is a valve by which you can isolate the tank from the system (there should be, but… they don't always get installed). Or it can be tedious, though still not really difficult.

If there is an isolating valve, close it and drain the expansion tank completely. If you are really fortunate, there will be a drain on the expansion tank feed line just for that purpose. Otherwise, you will have to physically disonnect it (unscrew it) from the piping; if you have to take that route, caution: it may be full of water, in which case it is going to be VERY heavy! Don't drop it! Once it is drained, then pump up the air pressure in the tank (there is a Schrader valve on the air end, just like a car tire) to the desired system pressure. Wait an hour or two and check that it is holding pressure. Then reconnect it to the system — thread it back on if you unthreaded it (use teflon tape like any other pipe joint) or just open the valve to the system. Then use the manual valve to bring the system pressure to the desired level.

If there's no isolating valve you are going to get wet. You still have to drain the tank… somehow… Now how to do that and how much of a hassle it's going to be (and how wet you will get) depends on what valves, if any, there are on the rest of the system — and how quick you are. If you have enough valves in strategic locations, you can close off most of the system so it doesn't drain, but without looking at all the plumbing I couldn't say which ones to close — or how successful that will be. You may be able to unscrew the tank and slap a cap on the pipe with minimal mess. I've done it, more than once.

If you have to drain the whole system down, that's a bore — as you will then have to purge the air out of the system when you get things put back together…

ChrisCS

Thanks! This is so helpful! I do have an isolation valve, which is good. How do I know the desired system pressure is? Is it just the pressure that I want the system to run at, and that matches the cold pressure reading on the gauge?

EBEBRATT-Ed

@ChrisCS

Most systems are set at 12-15psi when the system is cold. This is enough for a 2 story house. Unless you have 3 stories this is enough pressure. You should check the new ex tank before installation and set the air pressure at 15 psi befor you install it with no water pressure on the tank bladder.. Then when you fill the system you fill to 15 psi. When the water is heated it may rise to 25 psi or so.

ChrisCS

Thanks - so, my new expansion tank is already attached. So, can I detach it and adjust the pressure, then reattach?

mattmia2

Does this system also make domestic hot water?

How high above the boiler is the highest part of this system? Does the cold fill pressure need to be 18 psig?

ChrisCS

The boiler is in the basement, and it's a wall mounted unit, and it's a two-story house. So, roughly 23-25 feet would be the highest point above the boiler.

mattmia2

You can fill it to 12 psig. Ideally you'd check the precharge in the expansion tank, but try lowering the cold system pressure to 12 psig and see how high it gets when it is hot. The precharge in the tank may already be set for 12 psig and the higher cold fill pressure is causing your problem. You should check the precharge on the expansion tank about once a year anyhow.

Wall mounted boiler with 2 stories sounds more like 10-15 ft unless the emitters on the second floor are mounted on the ceiling.

ChrisCS

Good point, yes, they certainly aren't on the ceiling haha. Thanks! If I should check the precharge annually, is there a way to do that without removing the tank??

mattmia2

Put something like this valve between the tank and the system so you can isolate and drain it without emptying the system.

https://www.supplyhouse.com/Bluefin-BVT050HD-1-2-Threaded-Ball-Valve-w-Hose-Drain-Lead-Free

ChrisCS

Thanks!!!