Boiler not sending enough heat, should I change outlet temp set point?

dhw_probs

I have a wall mounted unit, on demand DHW & SH.

Hot water is fine, no problem.

When the outside temperature falls bellow about 20 degrees F, the unit isn't sending enough heat. Right now I'm set for 72 at the thermostat, morning outdoor temp is about 18 F, and a wake up to a chill in the house & 68 F on the thermostat.

I'm wondering if I should change the outlet SH temp on my boiler. It's currently set at 165 F, and the return temp is 150 F.

That seems like I have some headroom to go above 165 F, but I'm not sure, and don't want to damage the unit or the tubing that delivers the water to the heaters (mostly hydronic baseboard, but 4 old radiators as well that are about 30" x 48")

Zman

Is this the Lochinvar noble from your previous post? Is this a new problem?
There is generally no harm in turning the heating supply water temp to 185 or so. If the unit previously worked fine, it is doubtful that the temp is a problem.
Is there no outdoor sensor/outdoor reset on your system?

EdTheHeaterMan

Your boiler may have an outdoor sensor that is regulating the boiler temperature. that is called "outdoor reset." The outdoor reset has a range that is adjustable. If the boiler operated comfortably at mild temperatures but is not keeping up with colder temperatures the slope of the reset curve will need to be adjusted. Each boiler manufacturer has a menu that you need to go thru the adjust the curve parameters.

If you go too far on the adjustment, you will not get the maximum savings designed into the system. You will pay for more fuel than you need.

Are you using a setback (lower-temperature) at night?
One thing that ODR does not play well with is night setback thermostats. The water temperature in the radiators is enough to maintain a certain temperature. There is not enough heat in that water temperature to recover from a 5° of 10° setback that a standard old ON - OFF full temperature boiler would do.

So if you are turning the thermostat back at night, that may be your issue. Leave the temperature constant and the savings will happen automatically from the ODR and you can keep the same temperature all day and all night.

If you are not setting back
then look in the installation/operating manual or call Tech support for instructions on how to reset the ODR curve

dhw_probs

It's a Lochinvar cadet... Hasn't previously worked well either. I have this issue each winter. With a prior oil furnace the same radiator/baseboard setup worked fine, so I don't think it's that, and I'm at about 50btu/sqft, so the unit should be about 15% above necessary capacity.

I don't have a set back temp, it's basically 72F all day in the winter.

dhw_probs

@EdTheHeaterMan "the slope of the reset curve will need to be adjusted"

Thanks! that seems to have (hopefully) done it: I was only getting 165 F on the outlet so I assumed that was the set point, but when I dug into the installer settings I saw the maximum was actually set at 180 F, minimum 165F.

When I went further and looked at the reset curve, it was actually set for auto adjustment based on a 25 F outside temperature @ 120 F. Which is ridiculous, because it was telling the system to output 120 F @ 25 F outside temp. At least the minimum setpoint of 165 did an override so I was still getting something.

I think it was done by our previous HVAC guy (who we recently fired when he couldn't fix our DHW issue) because he told me once years ago he installed it something like "Factory settings had the DHW crazy high around 180F, I turned it down to 120." Which, very likely, No that's not the setting he changed.

In any case, I set it to 175 F , and the curve automatically calculated an outlet temp of 172, and I can already feel the difference.

Thanks for pointing me in the right direction!

EdTheHeaterMan

Awe Shucks, that's what we do here! Ye'r welcome.

dhw_probs

@Zman re: outdoor reset:

You were exactly right, as I detailed in my other reply, that was set to calibrate an outlet temp curve targeting a measly 120 F @ 25 F outdoor temp. Found the setting, fixed, and already see an improvement. Thanks!

neilc

As you stop shivering from years of cold operation there,
read up on your ODR,
you'll look to dial down the high and low supply water setpoints till the boiler just keeps the house comfortable in either extreme of outdoor air temp.
Here in southern Ct, zone 5, 180 at 5 oa, and 110 at 60oa work for my situation,
its a rough start point and dialing in to minimums can take a while (trial and error)

dhw_probs

@neilc thanks, I'll keep that in mind when the warmer weather comes around. I think my unit is set to 165 at 68 outside temp, which sounds higher than necessary... Unfortunately my (former) HVAC guy only admitted a few months ago that he hates our unit and wishes he never recommended & installed it. Actually, he said he feels the same way about all such high efficiency units, which would have been useful info to know before he recommended such a unit 5 years ago. 

neilc

read your manual now,
165 at 68 OA is way off, 100 at 60 OA is more like it,
and, well, we don't know where you are, so design temps vary by location, (ie 180 at 5 OA)
but most importantly you run the lowest effective supply water temps at either end of range to gain your best efficiency.
Learn you ODR range, make your adjustments thru the winter,
If you're cold when it's really cold outside, dial up the related setting (180 @ 5 OA), if your cold on a 55* day, dial up the (100 @ 60 OA). Go up 5 or 10* supply temp, if your cold on a 35* day, dial both water settings up 5.
shot in the dark, but, that 165 is probably good for your design day and 100 for 60 OA.
where are you located? and do you know your design temp?

hot_rod

dhw_probs said:

@neilc thanks, I'll keep that in mind when the warmer weather comes around. I think my unit is set to 165 at 68 outside temp, which sounds higher than necessary... Unfortunately my (former) HVAC guy only admitted a few months ago that he hates our unit and wishes he never recommended & installed it. Actually, he said he feels the same way about all such high efficiency units, which would have been useful info to know before he recommended such a unit 5 years ago. 

I have a Cadet combi in my shop, works great, super simple to program and work on. Very quiet with the poly foam jacket. It was a nice price point mod con.
All mod cons need to be piped and set up properly, ideally a yearly clean and service.
Sounds more like operator/ installer error??

neilc

let me add,
while you're learning your ideal ODR settings,
every Friday you set both ends of the supply water temp curve down 5 or 10 degrees on your way to best efficiency.
(until the cold comes back, then adjust as below)

neilc said:

read your manual now,
165 at 68 OA is way off, 100 at 60 OA is more like it,
and, well, we don't know where you are, so design temps vary by location, (ie 180 at 5 OA)
but most importantly you run the lowest effective supply water temps at either end of range to gain your best efficiency.
Learn you ODR range, make your adjustments thru the winter,
If you're cold when it's really cold outside, dial up the related setting (180 @ 5 OA), if your cold on a 55* day, dial up the (100 @ 60 OA). Go up 5 or 10* supply temp, if your cold on a 35* day, dial both water settings up 5.
shot in the dark, but, that 165 is probably good for your design day and 100 for 60 OA.
where are you located? and do you know your design temp?

dhw_probs

@hot_rod: Installer error. I don't know if he'd ever dealt with a high efficiency unit before. I think for him it was new & shiny tech and that's why he recommended it, much to his & my regret. He should have just told us he deals with less specialized ~80% efficiency units. We'd still probably have gone with him: He'd serviced our old oil boiler for a decade and was fantastic, responsive, and incredibly reasonable on price. Ditto for central AC unit we will still use him for.

Unfortunately it took a while to realize that he was totally clueless. One hint was when the system stopped working after his annual "service" so he came right back: it turns out he'd left the service manual on the air intake vent, so yeah, no air.

So, when the cold weather hit and we stopped getting enough heat, I figured f--- it. I read tech manuals all of the time, this unit is rates 20% higher than we need for our sqft, there's no reason we shouldn't get enough heat. I saw outlet temp should go much higher than I was getting, and posting here pointed me towards the right setting to fix it.

Unfortunately, I'm still having problems with the unit. I'm getting the inductor motor replaced in a few days @ $. I have little doubt that, after only 5 years, there's a decent chance it would have been just fine if the entire unit had been installed correctly to begin with and annually serviced properly instead of what this guy was actually doing. Earlier this year I had a DHW problem. Paid the guy $ ($ for the part) , and it worked for a day. I finally got in a reputable lochinvar-recommended service company, and when they checked out the DHW issue they said "Yeah, it just needed the standard annual maintenance, the ignition source was dirty and needed cleaning.

Long story short, I wish I'd taken the warning sights more seriously 2-3 years ago, but now I'm in good hands, and have a very good understanding of how to perform home-owner level adjustments and maintenance.