HTP Boiler short cycle

LRCCBJ

I have not been in discussion with them for more than five years now. I would ASSUME that the upgraded version is the only board available. I probably could ask them that question as to which is the current board available.

It does not have a problem under steady state conditions or slightly off steady state. In a situation with baseboards, it sends out water at the setting dictated by the outdoor reset. However, on a cold start, once the zone warms and hot water returns to the boiler, the boiler has a limited time to modulate down because of the narrowing DT. The original boards could not do this. They could not modulate fast enough to prevent a shutdown on HL. Of course, they would restart after one minute or so. Exactly what you don't want.

In the install that I am referring to, the situation was even more complicated by the use of a VT 2218. The VT would slow dramatically………..and fast………..when the DT narrowed. The original control could not keep up with with the VT.

You might not have these issues to the same degree with a fixed output circulator that cannot slow down when the RWT climbs.

LRCCBJ

You need to provide the p/n of the current board. I'll ask them how old it is and how far it was from the current board………….if I can get the fellow I was working with back then. It's been 7 years now.

joncroteau

https://forum.heatinghelp.com/discussion/comment/1827776#Comment_1827776

I’ll get that number in the am. Willing to spend the money if I can get a few more years out of this system.

LRCCBJ

The real question is the number of cycles. Can you get it to operate without cycling with the CH limit at 50%? If so, you don't need to spend the money on a new board.

Also, how many zones do you have? The boiler will struggle with a small zone that calls by itself unless it has the new parameters in the board.

joncroteau

When I set the ch to 50%, it cycled once (about 5 minutes to reach 175 degrees), ramped down to 135 degrees, and then fired again and maintained 165 degrees for over an hour. This was probably the longest I have ever seen a cycle on this unit. I have both zones (1st floor and second floor) set at 68. More often than not, the second floor zone is not calling because I think it is somewhat being satisfied with heat transfer from the first floor up the stairwell. .

LRCCBJ

Are you running on outdoor reset? It should not typically have a setpoint of 175F. That's excessive for most buildings unless it's close to design.

The 50% CH clearly helped.

If it made 175F in five minutes, then reduce the CH limit to 40 and run that for a few days. If you can't make temperature at the stats, you'll know 40 is too low………….but I doubt it.

joncroteau

no outside temp reset on this system. The boiler will only allow me 50% CH rate, no lower. Where should I start in terms of a water temperature setpoint?

LRCCBJ

Without reset, YOU become the resetter. 😁

I would start with 150F. See if the building will hold temperature. Since you are the resetter, you'll probably have to increase this value when it gets colder.

You probably still have the factory differential of 30F so, if the boiler shuts down on limit, you'll wait until it falls to 120F before it will restart (this is usually disconcerting to those who don't understand what the boiler is doing). This MIGHT be a bit undesirable, especially at very cold ambients if it does hit the limit. You can adjust this value. It's parameter 17bo.

The original board allowed the boiler a HL of only 7F above the setpoint until it shutdown. The latest board raised that to 12F. Very beneficial to prevent a shutdown.

joncroteau

excellent info. I’m around the house all weekend and can study (babysit) the boiler. It’s supposed to be a low of 8F this weekend so it will be a good opportunity to test the parameters.

LRCCBJ

I spent over 50 hours babysitting the original boiler back in 2016…………….four iterations of the control board with reams of data minute by minute to provide to HTP. They were quite receptive!

It was worth it. The boiler now runs from October to April without a shutdown. We left the basement zone 'stat at 80F to absolutely prevent a shutdown. Of course with reset, it never got above 75F or so.

LRCCBJ

It will be very interesting to see if you can hold temperature with an 8F ambient and a SWT of 150F.

Note that one thing you cannot do is a recovery. If you setback at night, the boiler will take forever to recover at 150F (unless the house it extraordinarily tight regarding air infiltration).

LRCCBJ

One more point for your experiment.

Presuming you are comfortable at 70F, raise the 'stats to 75F this weekend during the test. Watch the 'stats. They will tell you if 150F SWT is more than enough to hold 70F (if they climb to 72-73) or if it is insufficient (the 'stats fall to 68).

You will be pleased that the boiler will never shutdown once it stabilizes its SWT at 150F.

Record the ambient temperature and the 'stat temperatures. You'll need this data to develop a pattern for your manual resets. You can, if you're very ambitions, reset the boiler every day and keep it running all winter at your selected SWT (varying, of course).

joncroteau

https://forum.heatinghelp.com/discussion/comment/1828266#Comment_1828266

I don’t set back at all. Stats are set to 68 all winter. I will set the swt to 150 and see how it reacts. We built the house in 2016. It’s fairly tight but does lose temps over time . I have had the boiler lock out overnight and woke up to 58 degrees in the am (roughly 10 degree loss in 8 hours with an outside temp of 10 degrees).

LRCCBJ

I do believe you are on the right approach to get the boiler to operate without any shutdowns.,…………..basically the thermostat becomes superfluos if you have the patience to set it up properly. An outdoor sensor would greatly ease your task.

Set the 'stats to 75……………..😉

joncroteau

Data from the past 48 hours:

A)CH set to 150. Ambient temp of 9 degrees.
t-stats set to 75. After 5 hours, with an ambient temps rising to 24, stats could only make it to 72.
Boiler was firing at 149 degrees for one long cycle. Then, while watching it, it hit its temp of 154 and began its ramp down (flame off, internal and external pumps circulating until water temp came back near 125). It then fired up and modulated around 154 again. About 30 minutes later, it hit its mark again and began its ramp down. All of this was happening while it had a constant call for heat. This did not coincide with the second zone either opening or closing.

B) Set CH to 165. Ambient temp was 25 degrees. Both zones T-stats set to 68. Boiler acted the same as before. Long runs, interrupted a few times with hitting its limit, ramping down, and starting over. Mind you, the boiler isn’t shutting down due to overheat, it’s just meeting its water temp setpoint while the heat call is still happening. At this setpoint, the thermostats were satisfied throughout the night while ambient temps fell to 4 degrees.
C) as of right now, ambient temp is 10 degrees. The boiler has been running for two hours at around 154. Same ‘cycling’ as before (long runs, interrupted by some ramp downs.) House is maintaining 68 but the first floor has been calling the whole time.
Added a pic of the current setup. I have had more than a couple HVAC folks mention that my circulator is on the wrong side. The right hand side of the unit as you are looking at it is the return side. I installed new hi-vents last February, bled the system and made sure all rads were clean and clear. They all register pretty good heat (around 129 degrees)

In conclusion, we’ve greatly improved the short cycling issue that started this thread. However, the fact that I can’t raise 1800sq feet of house to 75 is concerning.

*don’t mind the camera facing the unit, that’s what I use to surveil it while I’m away haha.

LRCCBJ

Well done on the testing.

The first thing that needs to be addressed is the fact that you are concerned that you cannot raise the temperature to 75F. This needs to be explained carefully so you fully understand it.

Every building has a certain heatloss at a specific temperature. Let's say your building loses 30,000 BTUH when the ambient temperature is 8F. This will require the boiler to replace 30,000 BTUH. To do that you need a certain water temperature. I took a WAG and suggested you run it at 150F to see if it can manage to replace the 30,000 BTUH. What we observed was the boiler, at 150F, could replace all the energy lost in the building AT AN INDOOR TEMPERATURE OF 72F. You cannot get more than 72F with 150F water temperature. You also cannot climb at any reasonable rate when you start to approach 72F. It might take FOREVER TO CLIMB FROM 71 TO 72. The boiler output is limited by the 150F water temperature.

Now, if you truly desire 75F as your typical temperature in the space, you'll need to raise the temperature of the boiler to (WAG) 155F. Understand that it will take 48 hours to see if the building can make 75F. Of course, it will easily make it if the outside air climbs to 20F or so because the heatloss of the building drops.

So, please do NOT be concerned, whatsoever, if the building temperature will not climb. That is the normal situation for a mod-con. If you set the water temperature precisely, you don't need thermostats anymore. This is the ideal situation because the thermostat is not utilized and remains closed…………permanently. The boiler operates continuously without any shutdown (in theory if it has a proper control board).

Regarding it's propensity to shutdown when it climbs very slightly above the setpoint:

This is typical of the original boards. Way too sensitive to a shutdown if the SWT climbs only 5 degrees above the setpoint. In theory, the boiler should have modulated down BEFORE IT REACHED THE POINT OF SHUTDOWN. But, the original product was defective and it took us nearly 18 months to perfect it. The only way to fix that is to change the board. In theory, it should have been replaced under warranty. But, I doubt many installers understand such a situation and they probably have never done it (mine being the noted exception).

joncroteau

https://forum.heatinghelp.com/discussion/comment/1828614#Comment_1828614

Thanks! That’s excellent information regarding the building not climbing in temps under those conditions. I didn’t understand that concept previously. 68-69 is my preference for Temperature settings. So, it looks like I may be brushing up against the limits of this original control board in regards to obtaining one nice, long draw until all of the parameters are met and functioning as independently from the thermostats as theoretically possible. Sounds like a new board will get me there. Thank you so much for all of the information and knowledge. It’s truly appreciated.

LRCCBJ

Set the boiler to 146F and you will achieve 68-69 at current ambient. Of course, at a 20 degree ambient, the thermostat will open and the boiler will shutdown. You would need to manually reduce the SWT to 140F (WAG). This is the benefit of outdoor reset. It does it automatically for you.

The concept is inane for most folks. Don't fret about that.

The replacement board will cure the random shutdowns on limit. The outdoor reset will allow the boiler to run continuously…………..once you set it up properly (an iterative exercise that takes weeks of experimentation)………..and the boiler will thank you for it with extreme longevity.

You're welcome.