2 Radiators not getting hot, unless bled daily.

[Resipsa]

I have a two story house. Radiators on top floor work fine. Radiators on 1st floor all work except for two which are #s 2 and 3 on the supply from the boiler.

I have ruled out a blockage, as I'm able to get water flow at the bleed valves. Interestingly, the main supply and return lines are 1", but the branch supply / return to these radiators are reduced to 1/2 copper lines (1-1/2 Ts are used).

I'm at a lost as to why these radiators are not getting hot water, unless bled. Incidentally, ALL of the radiators have 1/2" pipes.

Any thoughts?

 

[Davie]

When you say you "bleed" the rads to get heat to them, do you mean that there is a significant amount of air which needs to be bled? Or do you mean that you let water flow out through the bleed valve?

If they are filling with air, then that's one issue, and would explain why they aren't getting hot (i.e. There's no hot water in the rads). If they are not filling with air, and the only way to get hot water to them is by letting system water run through the bleed valve, then you have a flow issue.

Another few questions: how long have you lived in the house? How long has this problem been presenting? And have there been any changes to the system in that time?

 

[Sponsor]

 

[Resipsa]

When you say you "bleed" the rads to get heat to them, do you mean that there is a significant amount of air which needs to be bled? Or do you mean that you let water flow out through the bleed valve?

If they are filling with air, then that's one issue, and would explain why they aren't getting hot (i.e. There's no hot water in the rads). If they are not filling with air, and the only way to get hot water to them is by letting system water run through the bleed valve, then you have a flow issue.

Another few questions: how long have you lived in the house? How long has this problem been presenting? And have there been any changes to the system in that time?

Great questions! Not much air to speak of, but essentially using the bleed valve to get circulating hot water to the radiators. At times I can "bleed off" 2 gals of water before hot water reaches the radiator.

Once the hot water reaches the radiator, it doesn't seem to recirculate back into the main supply/return.

I suspect that there is a flow issue, and ruled out the circ pump since the 2nd floor gets heat.

Today, I'm contemplating re-routing the supply/return lines into the crawl-space to reduce the extra long 1/2" pipes.

The current distance from the 1" lines to the radiators is approx 7'. When the system is running, only about 3' of the 1/2" lines get hot, hence the reason I opened the bleed valve to encourage the hot water to come thru the radiator.

Some point in the last 4yrs, it became necessary to open the valve to get hot water to the radiator

 

[Davie]

Well, that does narrow it down a bit.

I tend to agree with you that it is a flow issue. Sounds like the head loss on those two rads is significantly higher than the others. When you open the bleeder valve, you are creating a lower head loss path for the water to take, and thus bringing an influx of hot supply water into the rad. So the question is, What is causing the increased resistance?

Does this image look like what you are describing, where the orange lines are 1/2" and the rest is 1"?

And maybe this is an obvious question, but are you sure the radiator valves and lockshields on the two rads in question are fully opened?

 

[Dana]

Is it possible that this system is designed with mono-flow tees? A monoflow tee system has the radiators teed into a circulation loop, and the internals of the tees force some of the flow to be through the radiator rather than the main loop plumbing. As tees erode over time (several decades) they become less effective.

With a worn-out monoflow tee bleeding the radiator would bring hot water into the radiator, but wouldn't make water flow through the radiator.

 

[Resipsa]

So, I'm getting heat to those radiators now, without any pipe modifications. After some careful checking, it appears to be a flow / pump issue. There is another area in the system (basement, same level with boiler) that isn't getting sufficient water flow to heat another radiator (not previously mentioned in my post).

At the supply house getting a replacement pump. The old one is 30yrs old. It's not making noise, but the water flow isn't re- circulating properly.

 

[Resipsa]

Yes! The lines have what look like diverter Ts.
I just don't understand why someone woul choose to use 1/2" supply/return lines to radiators.

I'll fit the new pump, do some updating to the system, ie: scoop, vent, tank, pressure relief valve, etc while the system is down.

 

[Dana]

Yes! The lines have what look like diverter Ts.
I just don't understand why someone woul choose to use 1/2" supply/return lines to radiators.

That's because in most systems an individual radiator doesn't need more than 0.5-1 gpm of flow to work, and half-inch plumbing doesn't present much resistance at 1 gpm, no reason to go bigger. The bigger resistance is from the internal feature of a mono-flow tee.

 

[Resipsa]

That's because in most systems an individual radiator doesn't need more than 0.5-1 gpm of flow to work, and half-inch plumbing doesn't present much resistance at 1 gpm, no reason to go bigger. The bigger resistance is from the internal feature of a mono-flow tee.

Thank you!

 

[Resipsa]

So I have had quite the adventure since my last communication. I replaced the circ pump, which did not energize. It has turned out that there is an issue with the relay.

I did not suspect the relay because the contact would energize when the thermostat called for heat. This box also operates the circ pump. There's no voltage when I place a probe on the C1 terminal during operation.

I have opted to replace the existing box with a Honeywell aquastat with all the limit and circ controls...

QUESTION: the aquastat has a short sensor and therefore requires mounting on the boiler housing, but how do I install the "well?" The longer sensor makes sense as I could insert it directly into the pipe, but I have no idea what should happen to the sensor on the Aquastat. https://www.supplyhouse.com/Honeywe...lay-High-10F-Diff-Low-10-25F-Adj-Differential

 

[Jadnashua]

Without the circulator actually running, sounds like what heat you did get was via convection. Can't help you with mounting the sensor. A look at what you have and what you took out might help.

 

[Resipsa]

I had a talk with Honeywell yesterday. It appears that attempting to use a triple aquastat is futile, due to the boiler's age. There is a suitable switchable relay that has a transformer to address the low voltage requirement of the gas valve, and additional screws to accommodate 120v supply for the circ pump. Thx again for all your help.

 

[Resipsa]

Without the circulator actually running, sounds like what heat you did get was via convection. Can't help you with mounting the sensor. A look at what you have and what you took out might help.

Yes! I should have this all sorted by Monday.