Boiler not reaching desired heat levels

nikos88 · December 6

I have a Bosch SSB255 gas boiler with radiant heating 3 story property. The high set limit was set up at 180f with the low at 140. It’s a condensing boiler with one zone. The thermostat is in the same room at the boiler and it has an outdoor reset as per photo.

Live in Canada where it can get pretty cold. The issue lately has been that the heating in the apartments was not reaching desired levels. I have 8 units. The CH set point I set now at 194 as per picture with the baseline at 160. These values used to be 180 and 140. The outdoor reset has not changed. In previous years I have had no issues but this year something is off. I have automatic bleeders on the radiators in both apartments on the 3rd floor. I’ve bled the radiators in all units in an attempt to see if it will help. I never had to do this as the auto bleeders function well. Basically when I bled the system, there was no air in radiators. The pressure seems fine as per pic

but as you can see the desired temp still shows 138f despite my changes. So my question is, when I changed the high and low settings, did I have to adjust the outdoor reset values as well? Could there still be air in the system? The pressure seems a little high to me but some say it’s normal. I would assume the water temperature would be warmer than the 138 as it’s showing. I’ve had the unit serviced every year so there was not error codes or issues. It’s a 5 year old system. Circulating pump works. Apartments are reading 20celcius sometimes 21. I usually have it set to reach around 22-23 as the building is old and there is definite heat loss. The thermostat is in the boiler room at is set to 24 Celsius but I’m assuming that leaving it in that room where it is already warm, the call for heat is limited seeing at the 24 set temperature is reached pretty quickly. Should I move the thermostat into another area where it is not that hot? So many questions. Sorry for the long post

GGross · December 6

If the thermostat is satisfied the boiler won't run generally speaking, so if the thermostat is being satisfied but the other areas are still feeling too cold, you will either need to adjust the thermostat setting up, or move the thermostat to an area that is actually occupied. Not sure about your system but 40-50 PSI is not what I would expect to see, 18-20 would be the normal cold fill pressure for 3 story, if the relief valve is built for it then this isn't a real issue though.

Some other thoughts. When the heating is called for in at the thermostat zone, ALL zones turn on correct? if so you are now heating up a ton of water, the boiler probably reaches 100% fire rate, and does not hit setpoint before satisfying the thermostat. I know my boiler does this as I have several zones with no thermostats, so when the boiler calls I will watch it fire at 100% get about 30 degrees F below setpoint, thermostat is now satisfied and boiler shuts off. What this tells me in my scenario is that my setpoint is too high, I can heat my space with lower water temperature, and my boiler is sized well enough. I chose to leave mine alone as the areas are all an acceptable temperature and my boiler condenses pretty much the entire time. in your scenario let's assume its a similar situation, the boiler more than likely CAN reach that set point temp, however the thermostat probably kicks off before the boiler reaches that temperature, need to move the stat or add one somewhere else, ideally in an area that is not up to desired room temp.

Beyond that air can get trapped in radiators and be difficult to get out, if the boiler is hooked to an autofill, or has been drained and serviced, it is possible they have air trapped, bleeding doesn't always get it out they would need to be purged. If the rads still get warm during a heat call I would think the air is not the issue though. If I had to wager a guess I would say your thermostat is just satisfied and the boiler turns off. Run a new thermostat somewhere more relevant to the temp of the units, or run thermostats to each unit so each tenant can control their own heat

EdTheHeaterMan · December 6

If you want the thermostat to get the boiler room to a desired temperature that that is the perfect place for the thermostat. I don't think that is what you are looking for though. I believe you want the apartments to be comfortable. Am I Right? If so, then you may want to find a way to place the thermostat sensor in the apartment(s) in order to get the apartment rooms to be comfortable. Just an old man's ramblings about logical stuff.

There are thermostats that have the ability to use sensors from other locations to get the results you want. this is one that may have what you need and will also connect to your smart phone so you can easily adjust the temperature as needed without visiting the location https://rgesmartsolutions.com/Thermostats-and-Temperature/I-HONT9XXXX-01-WHIT-XXXX-V1.html

nikos88 · December 6

thank you G Gross. This makes total sense and I was thinking the same thing about running the thermostat elsewhere. Possibly in the central entrance area of the building. Maybe this is a stupid question but there is only one zone for this system so one circulating pump. I was under the impression that only one thermostat would be required for one circulating pump. Based on what you mention, can different thermostats be hooked up to one zone?

nikos88 · December 6

edheaterman, you are right. I want the apartments to be comfortable. This was never an issue as my previous boiler as it was oil fired and non efficient without an outdoor reset. I will have to get a better grip on this gas boiler and find a way to get the thermostat into a main hallway so that it will create the right temperatures uniformly!

GGross · December 6

https://forum.heatinghelp.com/discussion/comment/1825113#Comment_1825113

It is possible to utilize multiple thermostats that would all turn on the same pump. all spaces would get heat of course so the coldest area would end up operating the whole building anyway (more than likely) For the sake of your dilemma I would try just moving the thermostat to somewhere a bit more relevant to the heated space, boiler room might get hot too quickly.

EBEBRATT-Ed · December 6

Funny that it worked before.

GGross · December 6

good point, it might help to know if this is a specific complaint from unit, and what the temp actually is in that unit. Possibly new tenants? possibly a window not shut tightly that used to be shut? anything at all that changes in the spaces that are not controlled by their own thermostat will change the temperature in that space over similar outdoor conditions from previous years

EdTheHeaterMan · December 6

Remote sensors can be placed in the actual apartments and the sensors connected to the actual control in the boiler room. Thermostat is where no one can access the control and the sensors will be in the actual rooms that you want to heat. Not the hallway where a door left open when someone is bringing in the groceries will trigger the heater that will overheat the building.

You can set it up with more than one sensor and have the thermostat average the readings.

If you need to run a wire to the hallway any way just put the hole in the other side of the wall the is inside the living space. (Tell the tenants that it is a CO2 sensor to keep the tenants safe so they don't try to fiddle with it. If that is an issue)

bburd · December 6

Thermostats in hallways don't work to set a comfortable temperature for an entire multi unit building. Generally, the hallways are interior and not sensitive to either the heat loss at the perimeter, or the response of the heating system.

nikos88 · December 6

gentlemen you are all on point and very helpful. I like the sensor idea Ed but I think I will try moving the thermostat out of the boiler room and see if this helps.
GGross you are on point. This is new tenants. The temperature needs to be 21 C and I had readings of 20. It is slightly low but in years past it was not an issue. I have not changed anything on the system so I just found the loss of 1 or 2 Celsius was not from anything I changed. I’ll report back once I’ve moved the thermostat and see how that changes things. Thanks for all the feedback

EdTheHeaterMan · December 6

There are wireless sensors that can be placed in each apartment and connected to the actual control that adjusts the temperature. That is easier that running a wire to a room or hallway. You have options. Good luck with your project.

If you want more info on the remote sensors, just come back and post your questions.

hot_rod · December 7

apartments will have internal heat gains also. Cooking,, laundry, showers, lights, computers, occupants , occupant activity all add to the heat in a space

I don’t see a single thermostat location ever pleasing multiple apartments?

nikos88 · December 7

ok so the changes I made finally seem to have made some gains. The increase to 190 high limit and 160 low, with an adjustment to the outdoor reset has increased the temperature unilaterally in all units. I went into each apartment with readings of 22-23 Celsius on average. This however is not the ideal set up long term. I will be moving the thermostat out of the boiler room for sure. The system set up is old and I agree the one thermostat is not the ideal for all units. Can not please everyone. I purchased this multiplex apartment unit like this so I am going to make changes moving forward.

Ed I really like this idea of wireless sensors. I have eight apartment units so I may just put one sensor in each unit. Centrally placed in each unit of course. If you have any suggestions on where I should start with this project, I would be greatfull.

hot_rod · December 7

the sensors need to control something . Are there zone valves for the eight units? If so there must have been thermostats?

If the entire building is one zone one pump, what will control the individual rooms

Boiler not reaching desired heat levels

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