Heat only working consistently when DHW turned off

bwhite56

Hi All,

Been struggling with my Triangle Tube Prestige Solo 110 natural gas boiler for a couple weeks now; my hot water has worked fine all along, but it has recently decided to stop working at least once or twice a day at heating my hot water radiators. If I leave it alone (or if I'm not home) it will usually eventually begin heating again, or after resetting it a few times it would sometimes kick on again. But recently I discovered a way to get it working consistently: shutting off my domestic hot water at the boiler. Obviously this isn't a long term solution, but if I have no immediate need for water, it at least gives me reprieve from the 10 degree winter. I only tried this because I noticed when I'd reset the boiler, if it was going to start working again it would change to a status 3 on the display (Heating CH), but if it wasn't going to work right it would change to a 4 (Heating DHW). When it wasn't being reset and wasn't working it would just sit at 6 (Desired heat reached) despite getting a call from the thermostat for heat and the radiators being ice cold.

Can anyone guess at the root cause? I plan to call an HVAC specialist on Monday, but I'd be interested if it might be a common or fixable problem. I'd also be happy to provide more info if it would help. Thanks.

kcopp

it this the TriMax control or the older MCBA control?
Are you sure the T-stat id working properly? How many zones?

Zman

The DHW side of the MCBA controller can be finicky. Some DHW aquastats don't make a solid enough contact and confuse the boiler control. If you install a triangle tube temp sensor in place of you aquastat on tthe indirect that will solve it.

bwhite56

It's the older MCBA model, 1 zone. I'm sure the tstat is working; that was my first guess when it seemed like the boiler wasn't getting a call, and I wanted a wifi thermostat anyway, so I installed an Ecobee and can now see 100% when it's calling for heat.

Zman I believe I already have the sensor; at least the info display gives me a reading. I've attached some photos of my setup, for what it's worth.

kcopp

Did you have this issue before the new T-stat?

bwhite56

Yes, I installed the new thermostat hoping it would help; it didn't, but I can now at least prepare myself if I'm heading home to a 55 degree house.

Zman

If you are seeing the "3108" number when you scroll through the "info" menu (pressing the step button) you do have the sensor installed. Not sure which menu you are in when you took these pictures.
The terminals used for the DHW are the same for aquastat and sensor. There is a setting that is different when you use the sensor.

bwhite56

That was just standby, indicating the CH was heating up after I turned off the DHW, but I do get a reading when going to 3 in the info display.

Zman

bwhite56 said:

That was just standby, indicating the CH was heating up after I turned off the DHW, but I do get a reading when going to 3 in the info display.

Is it the likely water temp or jibberish?

Zman

It may be that everything is normal. The boiler has a function called domestic priority. It will stop heating the house in order to recover the water heater as quickly as possible. You can adjust the settings to establish a maximum amount of time that this priority will happen. Is this what it is doing?

bwhite56

It's water temp, I turned the DHW on for a while so the CH was just beginning to heat back up.

bwhite56

I don't believe so, given that at points it's let the house temperature go down to 52. When it's not working it will cycle between 4 (Heating DHW) and 6 (At desired temperature). I could understand DHW taking priority, but something seems to be wrong with it thinking that the CH is at the desired temperature when it hasn't been answering a call for heat from the thermostat for hours.

bwhite56

These are also times when the house may have been empty or no hot water used for 10+ hours, so there would be no immediate call for hot water.

Zman

OK,
I am leaning towards as issue with the t-stat.
I would jumper the heat demand (where the t-stat ties in) and try to eliminate a flaky signal from the t-stat as a possibility.

bwhite56

I have tried that and the problem is still there; heat with DHW off, no heat with DHW on. I feel pretty sure it's not the tstat, since I've had the exact same symptoms with two totally different ones.

Harvey Ramer

How about the pump to the DHW indirect tank? Is it working correctly? Are all the connections to the pump good?

bwhite56

So, knock on wood, I believe I've figured out the issue. Some of the comments here gave me a few areas to look into, and I eventually stumbled across this topic (http://forum.heatinghelp.com/discussion/147422/triangle-tube-prestige-excellence-110-no-heat) which sounded similar and convinced me to take a look at the DHW sensor.

When I pulled it out it appeared to not be seated in the slot, so I'm guessing it was constantly getting too low of a heat reading, prioritizing the DHW over the CH. it was also wire nutted for length, and one of the cables didn't appear to be well connected. After resecuring the wires and making sure the sensor was flush against the tank, my heat and hot water appear to be able to coexist again.

Thanks to everyone for the assistance.