Gv90 short cycling be and slow to heat house

Rob_55

New install. Gv90+5. Baseboard. Two stories. 3 zones. 2000sq ft.

Didn't notice lack of heating until recent crazy cold temps. House normally at 65. Set to 70 and after a few hours it was only at 68. Noticed boiler would cycle on and off but thought it was just the circulator / energy savings routine.

Watched it go through a cycle. Start at 150 degrees. Cuts off at 175 after a few minutes of heating. Drops rapidly back to 150 as circulator runs and flame is off. Raised temp knob to 185 from 180, but not much improvement. Also noticed electrical beeping after I raised temp. Got the guy who installed it coming tomorrow, but just curious what you all thought.

See video of the heating cycle. Weird beeping st 2:52
https://photos.app.goo.gl/kkVtZqEK3c3mQm8v1

JUGHNE

Someone here that is familiar with that boiler could answer if those pumps should be pumping up or down.

There have been some pump issues mentioned here today.

JUGHNE

Rob, could you do a video of your piping and pumps. (Move slow for old people please)
I had the early version of this boiler and the inlet and outlet were clearly marked on it. Don't know about the later generation that you have.

Rob_55

Here's a video of the plumbing. Hopefully video is slow and steady enough

https://photos.app.goo.gl/92m6zJbX1TVQELPy1

Rob_55

Also, I have the outdoor sensor

JUGHNE

IDK, there were no inlet/outlet labels on the boiler?

You should have the manual that came with this boiler.
It includes typical piping diagrams, perhaps not as involved as your piping but give the basic concepts.
Pumps have arrows on them indicating direction of flow.

Someone here can just look and know.

Rob_55

Looks like flow is correct. See attached

Ironman

There should be a big label on the side of the boiler that shows the connections.

The return goes to the secondary heat exchanger.

unclejohn

The boiler primary/secondary tees seem a bit far apart.

JUGHNE

I think his book says 12" max.
What started me on this crusade was the first video, when I paused it I could see 2 pumps pumping towards the boiler.
It is actually the pumps on the return pumping into the boiler rather then away after the boiler towards the zones.
That isn't quite right but doubt if it is the cause of the problem.

Maybe a control issue with the boiler mixing valve?

SeymourCates

@Rob

The boiler that you have can offer up 119 KBTU net.
The question that begs is whether the house can actually utilize 119KBTU. It would require you to have approx. 238 feet of element for the baseboard. This is impossible in a 2000 square foot house. This explains your constant cycling.

It' is, unfortunately, the typical situation of the "contractor" installing a boiler that is double the size necessary.

Ask the guy who installed it whether he ever did a heatloss on the house before selecting this boiler. See what he says.

Rob_55

Approx 140ft of baseboard + 50gal indirect super store water tank. My boiler gv90+5 is 113kbtu. Sounds about right based on what I read online. I'm pretty sure I watched him measure for this.

Ironman

You don't add the indirect into the sizing since it has priority.

Your BBs are only capable of outputting 70k btus at 170 AWT.

Rob_55

Ok..So assuming it is oversized, why won't my house heat up?. Baseboard barely gets hot. Wasn't a problem when it was warmer out as I could feel the heat coming off the radiator?.

Ross_7

Try turning the "Economy" setting on the control module to the "Minimum" setting. See if there is any change. Keep us posted.

Tom_133

I would also look at those pumps and see if they are blinking.
Happened again on a different job yesterday. Got there and found 2 zones blinking, its weird the 1 1/4" spirovent just sits there, I remove the head clean it and wham, it works again.

If you have the outdoor sensor, then the boiler will adjust the water temp based on that and some times that setting will be too low for the amount of heat that is required in the space.

Rob_55

Thanks everyone. One other thing that occurred recently was a water main break on our street. Not sure if losing water would do anything (air in lines).

Ironman

Rob said:

Ok..So assuming it is oversized, why won't my house heat up?. Baseboard barely gets hot. Wasn't a problem when it was warmer out as I could feel the heat coming off the radiator?.

If the boiler's over-sized, it can short cycle. IDK if that boiler has an anti short cycle timer. If it does, it's gonna hold the burner off for a minimum time, during which, the SWT to the rad's will cool down. They loose their heat output as that happens.

Ironman

Rob said:

Thanks everyone. One other thing that occurred recently was a water main break on our street. Not sure if losing water would do anything (air in lines).

What's the water pressure on the boiler gauge?

Rob_55

18psi

Beeping noise was coming from one of the circulator pumps.

SeymourCates

@ Rob

The reason the boiler won't heat your house is as follows:

The boiler operates with a 25F differential. This means it goes from 155F to 180F for each cycle. Notice, however, that it spends far more time between 165F and 155F as compared to the time between 180F and 170F. So, we can estimate that you have an AVERAGE supply temperature of about 165F when taken over the time interval.

Now, we must look at the average water temperature at the baseboard which is typically 6 degrees less than the supply water temperature: 159F.

This will not heat the house on a very cold day.

So, raise the boiler temperature high limit to 200F (boiler maximum). Then, the average water temperature at the baseboard will be approx. 179F and that will heat the house.

For efficiency in "normal" cold ambients, reduce the 200F value back to 180F and further reduce it to 160F in the shoulder seasons.

Rob_55

Thank you

SeymourCates

You're welcome.

And, because the boiler is so severely oversized, I would recommend that you get the "guy who installed it" to combine the three zones so a single thermostat (in the coldest zone) calls all three zones simultaneously. Have him install a globe valve in the two hottest zones and then monitor the temperatures. If either of the two hottest zones climb higher than desired, you throttle that zone with the globe valve to reduce the flow rate slightly. This takes some patience as the adjustments must be minute and the time to observe the outcome must be several days. Note that this approach is only valid for buildings that have reasonably proper balance between zones. It will not work if one zone is severely overradiated as compared to the other zones.

Rob_55

Turns out I had a bad water temp sensor. Temps are warm today, so we'll see what happens when it drops to teens tonight

stratman

The clip on return water temperature sensor?

lchmb

make sure to turn the boiler back down to 180. You should have no issues now..

Rob_55

Yes the return water sensor clip on