Radiant System not heating

iceman1337

We have a Geothermal system with a propane (Navien) boiler as the auxiliary. We have a Terra Therm M2-0152 control system and a buffer tank with pumps for the radiant in floor.

Normally after the in floor pumps have been circulating water the decrease in the tank temp will cause the compressor to turn on to warm things up. There is a secondary temperature threshold to turn on the boiler to auxiliarry heat as well.

For the last 2 days the in floor radiant has been calling for heat, which is running the pumps through the buffer tank, but the temperatures are continuing to decrease and the compressor or boiler have never kicked. Note I know this is not a problem with the Geothermal compressor because neither the compressor nor boiiler have had a call to turn on.

I have found this information on the control box https://www.pscia.com/ASSETS/DOCUMENTS/ITEMS/EN/m2-0152.pdf

The buffer tank temp and controls are via a TTI 152 control. Unsure where to find any details.



First, I am looking for help on how to override to get the system to turn on the compressor and/or boiler to get things warmed up.

Can I just supply 110V at the output of this controller? Should I attempt to match a resistance on the input? What can be done while I work on diagnosing the root cause?

Next, I need help on what to debug this problem with. My suspicion is on the thermistor, and if so how to get a replacement. I am looking for other ideas on how to help debug this.r

Zman

That controller is a rebranded Tekmar. If you need parts or instructions it would be easier to get them from Tekmar. https://www.supplyhouse.com/Tekmar-152-Two-Stage-Setpoint-Control-4151000-p

You should be able to see what temperature the sensor is reading by scrolling through the menu. If the temp seems inaccurate you probably have a loose or bad sensor.

If you pull the bottom panel and jumper from 3 to 4 and/or. 5 to 6 the heat pump or boiler should fire if they are operating correctly.

iceman1337

So I debugged and got the pumps running, but I am not getting hot water out of the buffer tank into the floor pumps.

I noticed there was no pressure on the tank. I went to add a bit of air to the expansion tank and there was liquid in the expansion tank. I am wondering if my liquid levels got low, or there may be an issue with my expansion tank.

I'm not entirely sure how to add water and purge air from my system. I see the air purging line on the top of the buffer tank. Just down from that is a water spigot up in the rafters. How do I add liquid and purge air from the system?

iceman1337

Jamie Hall

Water out of the expansion tank? Where? There should be an air valve on the tank -- a Schrader valve, on the end opposite the connection to the plumbing. If you got water out there, the tank is done and you need a new one...

iceman1337

It was on the schrader valve on the bottom of the expansion tank. I figured the bladder was probably shot, wasn't sure how to debug anything else.

Is this just unthread and swap out that tank?

Jamie Hall

Not quite that simple. You need to isolate the tank from the system (or drain the whole system... yuch0 and then precharge the new tank through the Schrader valve to the desired cold system pressure, then install the tank and reconnect the tank to the system and adjust the system pressure to the desired value with the manual feed.

iceman1337

I can't locate the fresh water inlet to my system. There is a spigot in the rafters. Is this to bleed the air or add the water in? I don't have any connection to inlet from my well, so I'll need to locate where to add water.

iceman1337

Or there appears to be a valve on the bottom of my Air Purger. Would that be a place to add liquid into the system?

iceman1337

Well, I found where to add water to the system by the boiler. We flushed through water on the buffer tank side and got the air out. Now it appears like we have an airlock somewhere in the floor loops.

hot_rod

The bottom valve is the purge valve, but the handle has to be installed properly as I think that version can purge from either direction. Does the small pump have a check valve installed in it? Or turn the upper valve off, fill there, purge from the lower valve.

If there is not a check in the pump, you may be filling on the top and flowing down to the purge.

iceman1337

I got all a new expansion tank and installed a new circulating pump while I'm at it, and a new air eliminator.

We used a transfer pump to add in more fresh anti-freeze into the system and purge the air from the lines. We got it to ~15PSI and the system is running and pumping. However, when the zones call for the pump to run our pressure almost immediately drops to nearly 0. We've run the transfer pump through a bucket of liquid until we say it run clean. I'm not hearing much more air purging from the air purger.

It seems that as soon as the zones stop calling the tank pressure increases a bit, sometimes up to 20 PSI. I had the buffer tank temp set higher (125°F) when trying to debug some of the issues. Right now I have it set to 100°F ±10°F.

Do we just let the system run a bit and add a bit more liquid to get the pressure up while running? Do I have something else going on in the system?

hot_rod

Did you check and adjust the tank pre-charge on the air stem before you installed it?
If you fill to 15 psi, set that tank pre-charge at 15.

Read the pressure on the system with an accurate gauge on the boiler or piping.

iceman1337

Our pressure gauge is right on the outlet neck of our buffer tank. Our expansion tank is just after the outlet, it was preset to 12 PSI. We purged the lines again and things seem to be more stable, but during pumping the pressure on the gauge sometimes drops to 0.

hot_rod

It seems the gauge in relation to pump/ expansion tank may be the issue? These examples show what happens when the expansion tank is located after the pump vs before. In some cases you can pull a negative condition by pumping at the expansion tank.

That high head Geo pump could cause that condition.

iceman1337

Things seem to be a lot more stable after we got all the air to purge from the system. We do have the expansion tank on the correct side of the circulator.