New hot water baseboard not getting flow

DIYOzzie

I recently replaced two hot water radiators with hot water baseboards. I did this a few years back on the first floor and now this project is on the second floor. One basboard is working perfectly but the other is stone cold. I bled the pipe and after all of the air escaped I got a weak stream of water. By feeling the pipes, I can tell that the water is coming from the return side. This baseboard is the furthest from the boiler, for what it is worth. The radiator I took out was working fine. The pressure in the system is about 15 psi. I tried cranking it up to 25+ but that did not help. Don't know what else to try. Any suggestions?

Ironman

Post some pics, but I hope you realize that a piece of BB won't have near the output of a cast iron rad.

DIYOzzie

The 1st picture is of the baseboard which is working just fine. Inflow and thermostatic valve is on the right and bleeder is on the left. The 2nd is the one which is not heating. Thermostatc valve is on the left and bleeder valve is on the right. I did pull the inline thermostat off to see if it was plugged or closed. It is open and water flows through it. You will notice that I used unions instead of hard soldering everything, just in case I had a problem and needed to pull the baseboard. Glad I did.

Regarding heat output, I was getting more than enough heat from the radiators. Fully open I could have gotten the rooms up to roasing temperature. I did not need that much heat.

Ironman

What's the piping like below? Is it a Monoflo system? Direct return?

DIYOzzie

I am not familiar with these terms but will describe the pipinig as best I can. A pipe comes up from the boiler (Weil-McLain) that carries the hot water out to all of the radiators. A parallel pipe carries the water back from the radiators to the boiler and goes to the pump which is on the side of the boiler.

Here are some pictures that should help:

Ironman

Looks like a converted gravity flow system piped direct return.

More than likely here's what's happening: when the system was original, it relied on gravity to move the water. There were no pumps back then on residential systems. This is why the iron pipes are so large. The heated water would rise because it became lighter than the cooler water in the pipes.

Somewhere along the way, a circulator was added and it became a forced flow system. Probably when the original boiler was replaced.

Water always takes the path of least resistance, and with those large pipes there's very little resistance. When you changed the rad's and put copper tubing with TRVs, you created a path of higher resistance and the flow avoids it because it finds less resistance in the larger pipes and rad's without TRVs.

Those old gravity systems were carefully designed, piped and balanced. You can't just marry a modern emitter, TRV and smaller piping into it.

The other thing I notice is that the TRVs are on different ends of the BBs. Are you sure you don't have one of them piped in backwards?

DIYOzzie

I know I do not have it piped backwards. I remember which side of the radiator the bleeder valve was on and also where the shutoff valve was. I also checked the pipes in the basement where they come off the main pipe and head up the wall. The feed is on the left where it enters the wall and the return is on the right. I even felt the pipes to make sure the feed was hot and the return was cooler. The rooms are on opposite sides of the house so maybe that is why they are opposite.

I am wondering how I can resolve this now. Take out the TRV? I was thinking of attaching a PVC 3/4" adapter to where the TRV is and fitting it with a garden hose adapter, then capping the return temporarily with a PVC adapter, to get the water flowing in the right direction. (I can shoot the water out the window.) But I do not know that it will keep flowing in the right direction after I connect it back up. Maybe a dumb idea but the only one I have.

BTW, the house was built in the 1940's. I did not think the system was that ancient.

Jamie Hall

I think @Ironman is right -- converted gravity flow. And if he is, as he says, getting it rebalanced so that those two baseboards heat properly is going to be a bear. Are there control valves on the other radiators? The ones which were there originally? Sometimes there are. If there are, and if they are operable, you may be able to get things balanced better by partially closing them. The objective of the exercise is to get the resistance to flow -- at the rate you want the flow for the heat you want from the radiator -- the same in all the radiators. This may take considerable fiddling, as changing one radiator will affect, more or less, all the others, but it can be done.

If there aren't valves, you may find that you will need to put throttling valves on the lines leading to the old radiators, to accomplish the same purpose.

DIYOzzie

I have replaced 4 upright radiators with baseboards. Of the two that I replaced several years ago (both on the first floor) on one I installed a control valve and the other I did not. The one without is in the room where the thermostat is, so I am not trying to keep that room cooler. The remaining two that I just did (in the pictures above) are on the second floor. One works fine with a contol valve and the other is the problem. There were no control valves on the original radiators.

Alan Welch

Try bleeding with the end with the bleeder lifted up , then try with the trv open, closed, pump running and pump off. You may find an air ticket is stopping flow.

DIYOzzie

Will give it a try. Williing to try anything.

DIYOzzie

Yesterday I took out the TRV and replaced it with two male adapters and and elbow, all in CPVC. Did not want to solder in copper yet, in case it did not work. At first I was not getting any flow, so I went to the boiler and opened up the pressure regulator on the inlet pipe, to take the boiler pressure from around 18 psi to 25 psi. I also closed the TRV on the 1st floor radiator which sits downstream from the one I was having a problem with, which essentially made my problem baseboard the the last one in the line. I started to get hot water coming through. And as of this morning it was still flowing. I just re-opened the TRV on the 1st floor baseboard and will see if I still get hot water flowing on the second floor. If all is well, I will drop the pressure back down to around 18 psi. I have decided that I can live without a TRV on this baseboard.

Leon82

I'm not 100% sure, but cpvc is not meant for heating. I would change it to barrier pex or copper asap

DIYOzzie

With regard to pressure and temperature limits, cpvc is within the limits. 100 psi and 180 F. I will monitor my boiler water temp to see how hot it gets. The guy at the heating place where I got my baseboard did not say anything about not using CPVC. The male adapter I am using is brass on the threaded side and CPVC on the other side where it connects with CPVC pipe.

Canucker

CPVC doesn't have any oxygen barrier that I'm aware of. That is the issue, not the temp limits