One zone not reaching set point

mikem31402

Hi All-

Awesome forum, I have learned a lot of the past few weeks reading all of the old threads. Trying to debug my own issue here.

I have an (old) gas Weil Mclain boiler. Seems to be working just fine. We recently had some cold weather in the north east (NY) and I noticed in one zone, we are never reaching the set point. And it is dropping well below set point at night (set at 70, reading 65).

Facts:
- Radiators are hot
- Zone valve seems operational. When I call for heat, I see the lever move and open.
- Other two zone are perfect. One circulation pump
- Both supply and return piping are hot. I don't have an no contact infrared thermometer though.
- I purged all zones thinking it could be air. There was some air in the line, but I've done this twice and nothing seems to change it.
- The one room is a tough room, its an extension with no basement. 3 skylights. high ceilings, and borders the garage.
- Room size: 15L x 23W x 10H (its 8-12 on a slant)
- Linear feet of baseboard: 18
- During the day, it does reach the setpoint of 70 sometimes, but I believe that's due to the thermal gain from skylights/sun.

It could just be that this room has crap insulation and should have more LF of baseboard. but I want to rule out any other possibilities. The previous owner said he never had that problem (which could be not true, but has no reason to lie). This is my first year in the house.

Really appreciate ANY input/guesses.


EDIT: Forgot to mention, I tried to figure out heat loss, but it didn't make much sense to me.

I have 16 ft^2 of Door to garage. 38 ft2 of a sliding door. And 8 ft^2 of skylights.

Thanks!
Mike

Jellis

has the current setup been working well? even on cold days?
what kind of thermostat are you using for that zone? if it has batteries you may try changing them and see if that takes care of the problem, would be a nice simple fix
what are your aquastat settings for the boiler?

mikem31402

Current setup has been working well (I think) but there was only a few cold days before this, so it's possible I just didn't notice.

Its a Nest thermostat. I beleive its working fine because when I increase the heat above current temperature, it does call for heat?

aquastat set at 180. Pressure at boiler looks to be around 14 (the taco "control" (don't know correct name) is rated for 12 PSI

Jellis

Were you in this house last winter during the horrible cold snap in January? Did the temp hold up then?
Make sure the baseboards are unobstructed and clean. 18' of baseboard will put out roughly 10,500 BTU's at 180'F which as you implied may not be enough for your room. An extremely rough heat loss calculation of your room size with no windows and doors calls for 8500 BTU/H.
I would start with an accurate heat loss calculation of the room which requires more information than provided.
I like this sheet myself
https://eminnetonka.com/images/permits/heat_loss_calculation.pdf

mikem31402

@Jellis thanks.

I didn't own the home last year. previous owner claims there werent any issues...

I'll try to work out that heat loss sheet, but I'm sure there is a good amount. 3 skylights, sliding glass door, borders the garage...

HVACNUT

Raise the aquastat to 200° and see if that helps.
No basement. Slab or crawlspace? If it's a crawlspace, is there access to insulate?
The floor is hardwood, tile, carpet?
Is the 18 ft of baseboard all on an exterior wall?
Slant/Fin 30 or equivalent should be enough to heat the room but with 12 ft at the peak, that's a lot of heat up there. Ceiling fan?

Now about the Nest. Its supposed to be smart. But its actually not so much. If it doesn't sense anyone in the room, it automatically lowers the temp no?
Go through the Nest settings and see if you can override that feature or any setback. Eco mode? I'm not sure. I only connect customer supplied Nests. For WiFi thermostats, I offer Honeywell.

Jellis

I agree with @HVACNUT raising the temp of your aquastat will give more BTU's/foot of baseboard, if the room is far away from the boiler that could also be a factor,

If lack of baseboard/ too much heat loss is your problem then the higher temp will at least make the temp issue better.

mikem31402

Thanks @HVACNUT .

Any risk in raising the aquastat?

This part of the house is over a slab. All of the baseboard radiators are on outside walls. Hardwood floor. Good point on high ceilings, I agree, definitely at least contributing to the problem.

I worried the same thing on the Nest, but I disabled Eco and removed all schedule on this zone. I'm fairly confident its holding its set point over night.Temp in room dropped to 63 last night (SP of 71). Very frustrating. Baseboards are hot all night and when I compare the feel to my other rooms, it feels about the same (very scientific)..

One thing to note: It looks like the pressure gauge has moved up a bit over night to just under 20 (~17/18) The taco fill valve is rated to 12. Maybe that tells there air in the pipes?

Question:

When purging the system of air, here are the steps I follow. Am I missing something? Or something out of order? Note, I only touch this problem zone, but maybe I should close all zones when I do this?

1. Move zone valve to manual open (and drop thermostat SP so it doesnt go back to automatic.
2. Shut return water valve
3. Hook up hose and open dain pipe. Let it run/remove air 2-3 minutes. Close
4. Let pressure fill back up
5. Open back water return valve

Zman

Here are a few things to check:

Do heat loss calc for room and compare it to radiators installed.

Verify that zone valve is staying open for entire heat call and that the nest is not cycling it.You could just leave it manually open for a night

Check that the coils in the base board are clean and not full of dust bunnies. Vacuuming it out can make a big difference.

Check that the area under the radiators has not been blocked by the carpet installer. This is pretty common.

Find a means of measuring the temp of the pipe and compare the temp in to the first radiator and the temp out of the last. If you post this info, we can determine if the flow to baseboard is adequate.

mikem31402

Thanks @Zman. I cleaned all the radiators, they were pretty dusty.

I also tried dropping the boiler pressure a bit. I closed the valve and just let out a little bit of water until the pressure dropped to 12-15.

I can now hear a lot of water running in the pipes and gurgling. So there is probably too little pressure now? Or maybe Air as I suspect. It is up to temperature now and holding, although its a little warmer today and I get thermal gain from skylights. I'll see what happens tonight.

I dont seem to have any bleeder valves at the baseboards. Wouldn't the auto air vent slowly fix that problem?

Jellis

now that you hear the "water" in the pipes that means there is air present in them and you will likely need to purge them to get all of the air out.
your air vent may get all of the air out but it is not very likely, they are meant to remove trace amounts of air introduced into the system via oxygen in the water, not large amounts of air.

mikem31402

@Jellis Thanks for the response. Regarding purging... Anything I'm missing?

When purging the system of air, here are the steps I follow. Am I missing something? Or something out of order? Note, I only touch this problem zone, but maybe I should close all zones when I do this?

1. Move zone valve to manual open (and drop thermostat SP so it doesnt go back to automatic.
2. Shut return water valve
3. Hook up hose and open drain pipe. Let it run/remove air 2-3 minutes. Close
4. Let pressure fill back up
5. Open back water return valve

Jellis

Sounds like you have the basic idea,

turn off power to your boiler before purging, you dont want circ pumps running or zone valves to open when you dont want them to
make sure you close all 3 ball valves on the return side when your purging

purge one zone at a time, you want to try to maintain pressure while purging, the lever on your water feed valve will help you do this.