Cast iron rads on single loop and monoflows suddenly quit working.

BeatByHeat

Hello all,



I'm semi-experienced in hotwater boiler systems, and my friend asked me to check out his parents house. They have a 2 story house, one zone for the 2nd floor, 1 zone that runs radiant on 1st floor and 4 cast iron radiators in the basement. This is not a very large house, and the loops are relatively small. The rads all come off the main line, into the rads, and back up into the main line, with a mono flow T (just one) on the supply side. I thought you needed two, but they swear this system has worked for years until recently. The radiant on the 1st floor, and the baseboard on the 2nd floor heat great btw.



I tried to bleed them but they have older Sparco purgers on them instead of a standard plug w/ key, and to be honest I had a hard time figuring them out. They barely let any water out (and I thought that if they were automatics they shouldn't have let any water out at all). His dad says that he's gotten them hot by bleeding them while it was running, but that they didn't stay hot.



I'm thinking of changing the bleeders on one of them to see if I can get it going, but other than that I'm at a loss. Pressure is good 15-20 pounds hot. Could this be a pump problem? Impeller wearing out or something?



Thanks, and any help is appreciated.

Gordan

Hot water doesn't want to go down on cold water

Yes, the configuration and spacing of the monoflo tees is critical for any below-the-main radiation. If it was working before, it was probably hanging by a thread. Have there been any changes anywhere ELSE since this last worked, such as some other emitter on the main being shut off (even partially)? That could increase the pressure drop across the main, leading to less flow, and potentially to no flow in a marginal situation like this. Try also allowing the system to cool down completely (set the gas valve to pilot or something) while the circulator is running - this should eliminate the buoyancy component from the flow resistance. At least until it heats up.

icesailor

Monflows, rads and a mess:

Sounds like a mess.

I'll bet that the upstairs is fin tube baseboard, the first floor is in-floor, in the original install. The basement zone with radiators is an add on, later. The installer of the basement zone didn't understand monoflows and didn't do them right. The main is probably sized improperly and the tees are probably wrong.

If the basement zone was added on, in my opinion, the problems are too complicated to DX on this forum. You need to hire a professional that knows what goes on and how these systems should work. And what is wrong with this one.

I would hope that this monoflow zone has its own circulator. The problem could easily be something like a circulator that is improperly sized. Or it is just piped wrong. 

BeatByHeat

@Gordan

There hasn't been any changes made to it, no. I don't mean that this has just been working for a while, I'm talking 10+ years. Would it be worth my time to change the bleeders? Maybe put a standard bleeder on it to get the water moving, and then swap that with an auto-vent?



Anything else I can try at least? (I will try letting it cool down, it's an oil system though, I'll just unplug the burner.)

BeatByHeat

@icesailor

Everything was in the house at the same time, more or less. The 2nd floor is cast iron baseboard, and I'm pretty sure the rads were an old dumpzone for a coal system years ago. It is in fact pretty crazily piped together... the rads and infloor radiant are together on the same line, but the infloor has it's own pump after it goes through a mixing valve. Just the fact that it worked for 10 years or more this way makes me think it has to be able to work again.

BeatByHeat

hm

I can't unplug the burner, it's an older Crown. How else can I make the pump run without heating the system? Can I kick out the control and jump the TT?

BeatByHeat

Tomorrow

Going to try everything I can to fix this tomorrow. I'm going to let it cool down as Gordan suggested (I'm going to be changing a pop-off valve on the boiler anyway, so that will be a good time.) I'm going to try changing the bleeders on the rads to see if it can get things moving too.



Any other suggestions?

Gordan

Having read your post more closely...

Allowing it to cool down may not help. Bleeding (a lot) would accomplish the same thing: get rid of the mass of cold water at the bottom and displace it with water that's closer in temperature to what's in the main. You may want to observe, when you're bleeding (or doing a cold start), which riser gets warm, or do they get warm equally. There may be an obstruction such as a partially closed valve, or sludge, or something along those lines.



Ultimately, the issue is that these radiators weren't piped properly. If you're draining the system anyway you may want to fix this. There should be a monoflo on both the supply and return side, with the venturi ends "pointing" outward, and those tees should be at least the width of the radiator apart.