Fluctuating Pressure in Radiant Flooring

Sprale

We bought a new-to-us home earlier this year and I've been seeing some fluctuations in the pressure in our radiant flooring recently (naturally this didn't happen back when we had the system inspected). I'll see the pressure rise to maybe 40psi or so, and other times it will drop to zero. It looks like there is a bleeder at the top right of the system, but I'm not sure it's bleeding enough air to correct the entire system.



The boiler is upstairs, the manifold is in an interior downstairs wall, and only the basement has heated floors. There was some work done to the slab downstairs, and in the process some lines were cut and repaired, I'm just not sure the plumber bled the system properly. What's the proper way to bleed a system like this? It's our first time living in a home with radiant heating.

Zman

I suspect the radiant expansion tank has either failed or has been precharged with the wrong pressure. If you tap on the tank and it sounds waterlogged, you have found the problem.

Sprale

We got notes from the company that installed the system and serviced it. Get this: "Needs ST-5 expansion ... selling home. Will let the next owner deal with it." That's awesome, I hope I never meet the jerks... I'll pick up a replacement soon.
I just bled each circuit, and when turning each valve off and on, I noticed that some of them leaked (and some more than others). I didn't see any water on the floor below the manifold before bleeding the system, so I'm not positive that was the cause of the fluctuating pressure, but its definitely on my to-do list now. Any recommendations on replacement manifolds? It's a 6-loop, 3/8" unit.

Zman

The leaks may have been exposed by the high pressure. Those infloor manifolds are notorious for leaking. I would either replace or have a solid plan and replace when needed. Stick with quality a manifold like Uphoner.

HVACNUT

I'm not understanding the piping.
That's a direct fired water heater with an internal heat exchanger? Is that right?
Is the radiant under street pressure or is there a PRV somewhere?
An ST-5 is a domestic extrol, factory charged to 40 psi.

JUGHNE

I had 3 of the Infloor manifolds in my house. Two developed leaks on the flow adjustment knobs or the "O" ring quick connects fittings.
After 22 years.
If you have the 3/8" ID (1/2" OD) tubing that I have, it may be Polybutylene (PB) Mine is red in color (PBOX), it has an oxygen barrier.

I changed the manifolds but had to transition from the 3/8 PB to 1/2" PEX. The only "approved" transition fitting I could find was 1/2 x3/8" reducing Union/PB. Watts AB-UP3515RB_1008.
These are slip joint unions resembling the collet connections your manifold has now. They are all above floor and have had no problem after 2 years of use.

PB tubing got a lot of bad press 20 years ago and is no longer used for radiant heating. I believe (hope) the issue was the fittings and not the tubing itself, (as I have hundreds of feet of it buried in concrete).

If you do not have the PBOX type then any ferrous piping or tanks are subject to rusting and sludge issues.
If that is the case then a heat exchanger is recommended to isolate those components from the effects of oxygen as a vapor entering the tubing. The sludge could eventually plug the tubing. If buried in concrete it should be addressed soon.

The in floor tubing I have will only see 12-15 PSI and not over 120 degrees. The tubing is rated for more but as in any product the less stress put on it makes it live longer.

Does your boiler provide hot water for the house faucets and also heat the floor? There must be a pressure reducing valve for the heating side of it to keep it at the 12-15 PSI.

Grallert

HVACNUT said:

I'm not understanding the piping.

That's a direct fired water heater with an internal heat exchanger? Is that right?

Is the radiant under street pressure or is there a PRV somewhere?

An ST-5 is a domestic extrol, factory charged to 40 psi.

I agree. Correct me if I'm wrong. I think the heating water and the domestic water are one and the same. So water use is going to affect the gauge pressure.? I've seen it done like that and always thought it was nuts. If that is the case that circ is not long for this world. I wonder if there is a fluctuation at your water fixtures. If that a domestic water heating loop you might have a wonky well tank or well pump.