Boiler return supply reversed??

mtnbktrek

Working on a Weil McLain gv-4 propane boiler has 4 zones - indirect hot water /1st floor /master BR/2nd floor

Problem :
Weak heat coming out of baseboards
Boiler cycling on/off
Return is way hotter than supply
Supply gauge struggles to hit 140*

Existing problems that have been fixed:
Expansion tank was water logged -replaced (pressure is at 13psi)
Pressure relief valve replaced (30psi)
Cleaned burner intake and blower
Replaced pressure/temp gauge on supply line next to boiler
Thought issue was aqua stat so that was replaced -set at 200*

The question:
Pulling my hair out - how come return is at ~180* mayb 200* while the supply is at 135-140*
System was just purged and I'm very confident there isn't any air in the lines. Never had an issues with this boiler until exp tank went.
Any ideas? Really trying to avoid calling in a tech.

mtnbktrek

System was installed around 2002 in new home

mtnbktrek

This is how system is plumbed basically - I have a spirovalve installed above expansion tank

mtnbktrek

That's exactly what I was thinking

Called Weil McLain they had me test circ pump voltage -checked out ok - guy said mayb blades wore or slipping rec'd I remove and inspect primary side

Yea pressure and temp gauge is working correctly
The pressure is where it should 12-15psi

Going to cool boiler and remove circs - will be back later this evening w results

hot_rod

Remove the pump from the housing with the two or four allen bolts. With the pump isolated and pressure dropped of course.

See if the impeller spins when powered. they can stick and shafts can also break.

Does that boiler still have a bypass valve under the hood?

mtnbktrek

Removed pump and added 120v to the pump and it just humms no rotation so fig I'd take it apart - pulled the cartridge out removed impeller while holding cartridge I used channel locks to grab shaft and free up after rotating it a few times it was spinning fairly free so put it back together and installed filled system bled some air fired it up works flawlessly - dunno how long it'll run for but at least I know what it'll be if I get those symptoms.

And yes it still has bypass valve.

Thx for the help all

hot_rod

That may be all it needs, a helping human hand. It might be wise to watch for a deal on a replacement, they often fail on the coldest nights.

mtnbktrek

Yeah was thinking of grabbing a spare cartridge - bypass is the same pump