Hot Water radiant heat system not outputting enough heat diagnosis help

homeowner1337

Hey all, I have a hot water radiant system - old house, with radiators. I replaced a lot of the pipes from the boiler to the radiators, and have am pumping away from the boiler. See picture for setup.

Recently, the system has been running at very low efficiency. The symptoms are:

• House is cold. Thermostat constantly asking for heat
• Boiler cycling between max heat and waiting to cool (170-220 F, when it shuts off)
• Pipes going out of the boiler are EXTREMELY hot
• Some radiators are somewhat hot, other are cooler
• Returns are much cooler/cold

My instinct says the pump is broken. What makes me question it is:

1. I've had a lot of issues with getting heat to properly circulate around this system (especially because I have two manifolds - I should probably have more than one pump)
2. This is sporadic. It happened the other day, then I messed with stuff (turned on/off valves, unplugged boiler, etc.) then things got back to normal

Any ideas? Thanks in advance.

Edit: I did bleed the radiators. I don't think it's an air pocket problem. But maybe?

GGross

Well the pump is installed wrong so it's a good chance it failed earlier than you'd like. They don't want the pump shafts to be vertical on those things. It's also some pretty darn small piping, how many BTU is the boiler rated for?

psb75

I think there should be a bit more separation between the circulator and the air separator. Also between air sep. and boiler.

jesmed1

What's your water pressure in the system? And when is the last time you checked the air pressure in the expansion tank and added air to it? They will slowly lose air pressure, and the air pressure is what governs you water pressure.

Also, what's the height of your highest radiator, as your water pressure needs to be high enough for the height of the static water column at least that high?

GroundUp

As was stated, the pump is installed wrong so it may have crapped out on you or may simply have air in the volute. 9 times out of 10, this is an air issue and bleeding the rads isn't always the solution- this may require an actual purge.

homeowner1337

Water pressure is 12 PSI, I have not checked the air pressure in my expansion tank recently. Boiler is rated for 109.1 Mbtu/hr, pipes are 1 1/4 to the manifold (I actually increased the size of those).

Can someone give a more detailed explanation of how the pump is installed wrong? Homeowner here, not expert :)

hot_rod

you need to add a purge valve like this on the return manifold

Turn pump so motor is horizontal

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homeowner1337

@hot_rod thank you, the image is so helpful. Is that valve different than the one I have? In the picture you can see a garden hose attached to it, it's just a regular garden hose valve (I think brass). I guess it doesn't have the second release valve.

hot_rod

You can build your own purge assembly. A tee, boiler drain and ball valve. The Webstone simplifies it with 2 connections instead of 4 or 5

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