HTP Boiler short cycle

joncroteau

Hello- I’m looking for some help with my HTP 80w boiler. I’ve had issues as of lately with the boiler reaching its setpoint temp, turning down, and then starting the process over again. This all happens in about 2-3 minutes. It’s not overheating, it’s just reaching its set point (174). I bled the system, verified pump operation and replaced the hyvent on the top of the boiler. The 2 zones are both maintaining the set temp of 68 but I’m just not sure this is normal operation. The boiler is for heat only and runs 2 zones. I guess my question is, should the boiler reach 174 and just maintain that temperature at low Fire until the room temps are satisfied or is the modulation i see normal operation? This particular system does not have an outdoor air temp sensor. Edit: boiler pressure is 18. 

mattmia2

Is this new behavior?

If it is there might be a strainer in there, make sure it is clear.

If not the setpoint may be too high, it will try to get to the setpoint as fast as possible, if the system can't get rid of that much heat it may shout down. You can limit the firing rate, if there isn't about 50,000 btu/hr of attached radiation I would turn the firing rate down to match what is attached to it.

joncroteau

It has honestly acted like this intermittently since install in 2017. There were a few times when it definitely had air in the system because it would boil very quickly and shut down with the high water temp error. The heated space is about 1500 sq feet. I will turn down the set point 5 degrees and see if I get that low fire maintaining. I’ve had enough issues with it over the past couple of years that I honestly don’t know what normal looks like. I have flushed the boiler a few times in the past few days so I don’t think there’s any blockages. 

mattmia2

if there is a strainer you have to take it out and clean it. But it sounds more like you need to go in the installer menu and set the max firing rate to maybe 50% or 75% so it doesn't put heat in to the system so fast.

joncroteau

I’ll dig into the manual and see where that setting is. I appreciate the insight. Where would the strainer be located if it had one? 

mattmia2

You'll have to look in the parts diagram in the manual and see if there is one. i have a uft-100 but i've never needed to know if it has a strainer.

joncroteau

The manual shows I can adjust combustion rate. Is that the same as firing rate? 

Ironman

There’s no strainer on that boiler, but lowering the firing rate may help.

It appears that you only have 3/4” piping connected to the boiler. If so, that’s only good for 40k btus.

What type of radiation do you have? Fin tube baseboards? If so, measure the linear feet of ELEMENTS (not the enclosure) that you have and multiply that by 500 to get the total btu output. It’s probably less than 50k.

The firing rate can be limited in the control. There’s also a step modulation function which should be turned on to help with this issue.

joncroteau

Yes, fin tube baseboards. I’ll give them a measure. There’s a combustion rate setting in the controls. Is that the same as firing rate? 

joncroteau

After doing that calculation, I come up with 27,800. For what it’s worth, the second zone only calls for heat about 75% of the time compared to the first zone. 

GroundUp

Keep in mind that you may simply be short cycling the unit if one zone is calling for heat without the other, and that zone is drawing less than 8,000 BTU. Any idea how many linear feet of element are in each zone? Perhaps one may be under/around 16 feet?

joncroteau

Zone 1 is about 32.6 lf
zone 2 is about 22.8 lf

Ironman

joncroteau said:

Yes, fin tube baseboards. I’ll give them a measure. There’s a combustion rate setting in the controls. Is that the same as firing rate? 

Parameter 18 is the firing rate and parameter 37 turns on the step modulation.

Hot_water_fan

You’ve got the best sized boiler you could do, now it’s a question of getting it to run as long as possible. It should have a few settings to do is: delay ramp, anti-cycling, and max output are three that are pretty common. 

EBEBRATT-Ed

Or add a buffer tank

joncroteau

I think I’m going to start to price out a new system altogether. This HTP has been problematic since install. 

KC_Jones

joncroteau said:

I think I’m going to start to price out a new system altogether. This HTP has been problematic since install. 

If it's a setting issue, you will need to get the settings right with any new boiler as well, so a new boiler doesn't seem like the solution to me, based on what you've posted.

pecmsg

joncroteau said:

I think I’m going to start to price out a new system altogether. This HTP has been problematic since install. 

9 times out of 10 that’s a installation / setup problem . Replacing the unit won’t help

mattmia2

I have a uft-100 that I have had for about 5 years now. The only issues I have had with it are an issue with some off gassing from the insulation around the HX until I ran it up to 180 or so once and a very occasional stored error code about the fan speed that doesn't cause any noticeable issue other than the stored code. I think it is some sort of firmware bug involving power up or maybe momentary power interruptions. @ironman has installed many of these and had little problem with them.

Ironman

The problem is NOT the boiler. It’s the fact that the installation wasn’t done correctly.

Make the suggested parameter adjustments and your issue should be mitigated.

If necessary, add a buffer tank as Ed suggested.

As mentioned, any mod/con is gonna have the same issues unless it’s setup correctly.

joncroteau

Ironman said:

The problem is NOT the boiler. It’s the fact that the installation wasn’t done correctly.

Make the suggested parameter adjustments and your issue should be mitigated.

If necessary, add a buffer tank as Ed suggested.

As mentioned, any mod/con is gonna have the same issues unless it’s setup correctly.

I am going to dig into the all of the adjustments you suggested and see if I can get it tuned. Came home to a cold house again today. This time it was an ignition failure. I just replaced the ignition last week. The irony is that in the 2.5 hours it took to get the house back up to 69 from 61, the unit hit its target temp, went into low fire and just purred the whole time. 

mattmia2

when was it last checked with a combustion analyzer?

Redbaran

With the house "cold" ie 61F - 69F; the boiler had a "load" more in line with how it's currently setup - This proves that adjusting firing rate and modulation will help match the boiler to the system - low mass wall hung boilers are great; and most come with wide programming functionality - it's up to the installer to understand that and fine tune those parameters.

joncroteau

mattmia2 said:

when was it last checked with a combustion analyzer?

It hasn’t ever. I’m setting that up with my local hvac company. The boiler also throws ‘no ignition’ codes so I will have them check the pressure as well. 

joncroteau

joncroteau said:

mattmia2 said:

when was it last checked with a combustion analyzer?

It hasn’t ever. I’m setting that up with my local hvac company. The boiler also throws ‘no ignition’ codes so I will have them check the pressure as well. 

mattmia2 said:

when was it last checked with a combustion analyzer?

Any idea what the normal parameters of the combustion test would be? 

mattmia2

joncroteau said:

joncroteau said:

mattmia2 said:

when was it last checked with a combustion analyzer?

It hasn’t ever. I’m setting that up with my local hvac company. The boiler also throws ‘no ignition’ codes so I will have them check the pressure as well. 

mattmia2 said:

when was it last checked with a combustion analyzer?

Any idea what the normal parameters of the combustion test would be? 

it is in the manual

it must be set up with a combustion analyzer when it is installed. if the combustion isn't adjusted right it is likely to not ignite sometimes. if it has been running for years like that it likely needs soot cleaned out of it too

joncroteau

joncroteau

This was in low fire. Tech checked on high fire and said it was right in the range. He also dialed the gas pressure up to 10.9. It was 9.56 when he started. Also checked the inducer and that was clean and in tact. 

pecmsg

131.9*f  stack temp?
PVC’s only rated for 140*f

mattmia2

is this propane?

there is a min spec for the propane pressure and i think it is a lot less than that so adjusting the house regulator doesn't seem necessary.

if it is lpg something could be happening with your system that it is not supplying enough pressure after an extended draw or in very cold weather.

joncroteau

Yes, Propane. He adjusted this on the gas valve on the boiler. It’s relatively warm here for this time of year. Not entirely sure where to go next.

mattmia2

The pressure is just measured at the boiler, if it needed to be changed that would be at the house regulator. The adjustment for the mixture is made at the gas valve.

The procedure is on page 47.
https://www.htproducts.com/literature/lp-542.pdf

Moisture in the propane or a low or too small for the size of the draw tank or ice plugging the regulator vent or piping that is too small for all of the loads can cause the propane supply pressure to drop.

Has it been opened and cleaned regularly?

I think there is also a recall on some versions with a plastic flap in the exhaust that could break loose.

joncroteau

mattmia2 said:

The pressure is just measured at the boiler, if it needed to be changed that would be at the house regulator. The adjustment for the mixture is made at the gas valve. The procedure is on page 47. https://www.htproducts.com/literature/lp-542.pdf Moisture in the propane or a low or too small for the size of the draw tank or ice plugging the regulator vent or piping that is too small for all of the loads can cause the propane supply pressure to drop. Has it been opened and cleaned regularly? I think there is also a recall on some versions with a plastic flap in the exhaust that could break loose.

Interesting. I did have the gas company out 3 weeks ago to address a gas leak on the regulator outside (the no-ignition troubles started shortly after) I noticed that he broke the plastic vent tube on the regulator and kind of just shoved it back in its place. I’ll check it in the am to see if that vent is clear. I don’t believe the piping is the issue as the furnace ran for 6 years without having the ignition issue. 

mattmia2

The vent can get blocked with snow or ice if it isn't arranged so it is protected.

neilc

mattmia2 said:

The vent can get blocked with snow or ice if it isn't arranged so it is protected.

or the rtv the tech stuck the break back into the hole with

LRCCBJ

joncroteau said:

It has honestly acted like this intermittently since install in 2017.

When the boiler was originally designed and initially delivered in 2015, it had serious issues with the control logic. The boiler could not modulate quickly enough before it reached +5F. over limit. Then it would shutdown on limit and restart about one minute later.

HTP made several iterations of that control over the two years between 2015 and 2017.

When done, the boiler could respond properly to an instantaneous closure of two zones (out of a total of three) and it would NOT shutdown on limit. HTP decreased the response time for modulation and also increased the the margin to +12F over setpoint before a shutdown occurred.

The final result was truly excellent from the original starting point.

Sadly, most installations of this boiler in that time frame will suffer from the poor control logic and none of the installers can do much about it.

You can mitigate the issue to some degree by reducing the CH heating capacity. This is parameter 18:cb on the display. If you can heat the building with 40K BTU's (likely) set the parameter at 55. It's much easier for the boiler to modulate down from 40K then from it's maximum (72K). Step modulation (37:CM) will not help with this issue.

However, understand that this approach will severely limit your capability of recovery if you are inclined to reduce the building temperature overnight.

If you were to replace the control board, all issues would disappear.

joncroteau

LRCCBJ said:

It has honestly acted like this intermittently since install in 2017.

When the boiler was originally designed and initially delivered in 2015, it had serious issues with the control logic. The boiler could not modulate quickly enough before it reached +5F. over limit. Then it would shutdown on limit and restart about one minute later. HTP made several iterations of that control over the two years between 2015 and 2017. When done, the boiler could respond properly to an instantaneous closure of two zones (out of a total of three) and it would NOT shutdown on limit. HTP decreased the response time for modulation and also increased the the margin to +12F over setpoint before a shutdown occurred. The final result was truly excellent from the original starting point. Sadly, most installations of this boiler in that time frame will suffer from the poor control logic and none of the installers can do much about it. You can mitigate the issue to some degree by reducing the CH heating capacity. This is parameter 18:cb on the display. If you can heat the building with 40K BTU's (likely) set the parameter at 55. It's much easier for the boiler to modulate down from 40K then from it's maximum (72K). However, understand that this approach will severely limit your capability of recovery if you are inclined to reduce the building temperature overnight. If you were to replace the control board, all issues would disappear.

That is great information, thank you. I have had other issues in the past that could not be readily solved by technicians or tech support. They seem to mitigate on their own but some others pop up here and there. I’m trying to do everything mechanical before I think about a new control board however the thought of this working flawlessly is tempting. I am going to follow Ironman’s advice and turn on step modulation as soon as I solve the ignition issue. I leave both zones on 68 throughout the heating season and never touch the t-stats. 

LRCCBJ

The step modulation will likely not help your issue and will delay the response to the building. You want the boiler to immediately go to whatever level is necessary to heat the building on the design day. If your heatloss is 40K, that's all the output the boiler requires. The CH limit will accomplish this.

I believe you will have quite a bit of success with a CH limit of 55 (assuming a 40K heatloss).

I guarantee that you will have success with a CH limit of 45. HOWEVER, you MIGHT need to raise it if you get near the design day. Remember I am making an assumption on your heatloss. If you know what you have you can calculate the CH limit appropriately. Figure the output of the boiler is 70K and calculate based upon your own heatloss for the building.