Navien Combi has DHW but no heat

IanPoirier

I bought a house this summer, small, single zone baseboard. We had a cold snap for a couple days and the heat worked fine. Hadn’t used the heat since until last night and it’s not working. The thermostat is a cheap Honeywell. About a month ago I lost power and happened to notice the screen on the thermostat was blank. I popped it off the base, didn’t change the batteries, and put it back on and it lit up again. Last night I put new batteries in since cold weather is coming. 

I’m not very familiar with these systems but I’ll try to explain what I’m seeing. When I turn the heat on the zone controller comes on and the circulation pump it’s connected to starts. The boiler doesn’t fire though. Could that be a thermostat problem. I’m getting a new one either way but I’d like to know if that’s the issue or it’s something deeper. The thermostat has three contacts. Could I jump them to test it? And if so which ones?

Jamie Hall

Not a thermostat problem if the zone controller and pump work properly. It might be a problem with the zone controller not getting the word to the boiler-- or, if the boiler is already warm from, say, a domestic hot water demand, it could even be quite normal. The test there is does the boiler eventually fire up if the heat is left on for any length of time -- say half an hour?

IanPoirier

I believe it’s been on for over a half hour because it took me a while to notice that the house wasn’t warming up. I can test that when I get home from work today. Another thing I noticed is that if I turn hot water on in a sink then check the boiler the DHW symbol pops up on the screen. If I turn on the heat the heating symbol does not show up. 

The previous owner left a box of manuals and warranties and such. I’m hoping the manuals for the system are in there. It was so late last night that I didn’t have time to go through them. The only other thing I noticed that may be odd is the zone controller has two lights, red and green. Both are illuminated. I’m not sure if that’s normal. 

HVACNUT

If the zone control is a Taco SR501, then the green light should always be on, and the red light is on when R-W closes for a heat demand. 
In the SR501, terminals 5 and 6 N.O. should go the the boilers low volt thermostat terminals. 
Are there any fault codes showing while in heat mode?

IanPoirier

No error codes. The heat mode icon actually doesn’t come on. Unlike the DHW icon which illuminates as soon as a hot faucet is turned on. 

IanPoirier

It is a Taco SR501 and thank you! I checked the terminals in the Taco, all good. Then I checked in the boiler and one of the thermostat wires going into the low voltage terminal was just loosely sitting in the screw housing thingy. I don’t know the proper term for that type of terminal. But the screw wasn’t tightened at all. I cranked it down tight, turned on the heat and it started right up. I can’t believe it was a loose wire. I don’t understand how that terminal wasn’t tightened down during install. Either way, it’s working now. Thanks for everyone’s help. 

HVACNUT

Glad it worked out. 
If you're not familiar, and since you're new to the house, it would be wise to have maintenance done on the boiler with a  combustion analysis.

IanPoirier

I’m definitely not familiar with Naviens so, yeah, I need to do that.