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Bosch Combi 151 Several Problems

sbnycsbnyc Posts: 5Member
We had a Bosch Combi 151 installed aprox 2 years ago and have had ongoing issues. Since it started to get cold this past Fall, the unit has been unreliable.

We're on propane, the house is a forced air system, and we use a Nest thermostat. It's a weekend house, so we keep the Nest on eco for most of the week.

I'm not sure if we have a single issue here, or multiple separate problems.

The primary issue is that the system will blow cool air for quite a long time when the Nest is set to 72. Over several service calls, the installer was unable to replicate the issue. One of the service guys simply set the two dials to max I suppose assuming this would raise the temperature quicker and eliminate the cool air issue. It did not work. This same technician informed me that the valve on the back of the unit needed to be replaced, which was recently done.

On the most recent service call however, a different guy from the installer did in fact see the issue - the pipe leading to the air handler was not hot, when it should have been. He was able to determine that a valve inside the unit was not switching back over to heat after being switched to hot water. He adjusted this valve and the appeared to fix the issue. Unclear if it is actually resolved fully, but we appear to no longer have that particular problem. However, he also reduced the two nobs on front to lower temp levels - and now I am noticing that when set to 72, the temp never quite gets there - it gets to about 68 after staying on for a long time - then shuts off.

The second issue is the condensate pump - or the valve that leads to it - appears to have some issues. The pump turns on randomly every hour or two and makes a fairly loud noise for maybe 10 seconds. I can hear it from the living room above where it is in the basement. On a recent visit to our house, shortly after turning the temp up on the Nest (after it was on eco for the week), the pump was making quite a bit of noise, so I went to check it, and it was splashing water all over the basement floor, and the pipe coming from the back of the boiler was shaking repeatedly. Today, this happened again - loud noise from the pump - went downstairs to check, and water was splashing and the pipe was shaking. Unclear if this is related to the valve issue above or not.

Im really not familiar with this technology so im really just trying to understand are these common issues? Is the pump issue possibly related to the valve that was replaced? Is the pump and valve issue connected to the internal valve issue (the one that switches from hot water to air and back)?

If the forced air is no longer getting us past 68 degrees, is that due to the dial setting on the front of the unit?

Is there any reason we wouldn’t increase this to 5.5, 6, or max for hot air? Would this dial setting have anything to do with the valve/pump issue?

If feels like we have a ton of problems here - im trying to be patient with the service tech guys, but this issue has been ongoing for many months now.

Any advice?

Comments

  • SuperTechSuperTech Posts: 1,126Member
    Please post some pictures of your equipment. What you typed about valves going to the condensate pump and water splashing doesn't make sense to me. The boiler should just drain condensate into the pump by gravity, no valves involved. Water should never be splashing anywhere. Perhaps the drain trap in the boiler is dry ? Pictures would be a big help, I'd like to see the boiler, all piping around it as well as the air handlers and hydro coils.
    The air handlers should probably have an aquastat control on the pipes to the coils to keep the fan off until the hot water reaches the hydro coils.
  • nicholas bonham-carternicholas bonham-carter Posts: 8,074Member
    edited February 8
    Maybe you need alternative service people looking at this. Are the present service people the original installers? Are they recommended by Bosch?
    A competent service man would methodically inspect the installation, and verify that the manufacturer’s instructions had been followed, and, following the Service manual, and its diagnostic “tree diagram”, address and cure the problems, one by one. Vibration may be caused by a broken fan blade. These problems should not have lasted for years as opposed to days.
    As SuperTech notes, the system should never blow cold air.
    There may be an outdoor reset feature setup, which varies the heating loop temperature, as a function of outside temperature, and in warmer periods, this may make recovery slow and problematic, after a Nest setback.—NBC
  • IronmanIronman Posts: 5,451Member
    As far as the 3 way valve that switches between domestic and space heating goes, there is no adjustment on it. So, we don't know what's been done there.

    As far as the pipe "shaking", more info and pics are needed as mentioned already.

    You need to get rid of the Nest; it should never be used on a modulating boiler or appliance as it logic fights with the logic of the boiler and its OutDoor Rest function (ODR). That's why you're having trouble getting above 68*.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • SuperTechSuperTech Posts: 1,126Member
    edited February 8
    Just because it is possible to install a Nest thermostat on a boiler, doesn't mean that you should.
    In the majority of the times it's completely inappropriate for the application.
  • MikeL_2MikeL_2 Posts: 216Member
    I would check with the boiler manufacturer to make sure the unit is compatible with smart tstats.......
  • IronmanIronman Posts: 5,451Member
    MikeL_2 said:

    I would check with the boiler manufacturer to make sure the unit is compatible with smart tstats.......

    That may or may not get a correct answer since a lot of people on tech support lines simply use flow charts and have no real field experience.

    What I said about the Nest comes not only from multilpe experiences where I've gone behind others that installed them, but also directly from Bosch training classes where they specifically said NOT to use a Nest or any other "smart" stat.

    This issue comes up on here almost every week and the experienced pro's on here give the same answer: don't use a Nest on a hydronic system, especially on a mod/con.

    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • nicholas bonham-carternicholas bonham-carter Posts: 8,074Member
    In these modern condensing boilers, the temperature setbacks can often be programmed into the boiler, and in some cases, through the internet.
    Other makes of thermostat which are WiFi connected may be approved for the Bosch, but apparently not the Nest, which was not designed by heating experts, but rather by computer programmers, with little knowledge of how these hydronic systems work.
    Some Honeywell thermostats may be compatible with the Bosch, but because of the outdoor setback, will need maybe 24 hours to recover the inside temperature. Outdoor reset will achieve great economy when set at a constant indoor temperature, but as said, may have trouble regaining the regular indoor temperature in a short period of time, unless they have a boost setting.—NBC
  • sbnycsbnyc Posts: 5Member
    Thanks everyone for the responses. I will post photos next time im at the house in a couple of weeks. I am posting a link to a video of what the Condensate Pump has done a couple of times now (shaking and spilling water on the floor). Beyond what you see in the video, it also starts up for a few seconds every hour or so, even when the heat is off.

    https://www.dropbox.com/s/6ore83flgpr4xqx/IMG_2443.MOV?dl=0

    @SuperTech – is installing an aquastat control on the air handlers something my installer would typically know how to do? Is that a pretty common installation?

    @nicholas bonham-carter – I was thinking the same thing - I should probably get another installer out to take a look. I have not reached out to Bosch yet.

    @Ironman – Im not exactly sure what he adjusted but he said whatever it is that switches back and forth between the two needed some kind of adjustment and that has seemingly helped with the issue of heat not working after running hot water.

    The reason we use a Nest thermostat is because we are 2 hrs from the house, we rent on Airbnb, and we need the ability to adjust the temperature remotely. It would be a problem if we were unable to do this. I figured the issue with not getting above 68 was because the temp knob was set lower by the repair guy. I have since increased it to around 5.5 and the temp now gets to 70. Is it absolutely for sure that using a Nest is problematic here?

    Thanks for all the feedback here. Super helpful.
  • IronmanIronman Posts: 5,451Member
    sbnyc said:


    @Ironman – Im not exactly sure what he adjusted but he said whatever it is that switches back and forth between the two needed some kind of adjustment and that has seemingly helped with the issue of heat not working after running hot water.

    The reason we use a Nest thermostat is because we are 2 hrs from the house, we rent on Airbnb, and we need the ability to adjust the temperature remotely. It would be a problem if we were unable to do this. I figured the issue with not getting above 68 was because the temp knob was set lower by the repair guy. I have since increased it to around 5.5 and the temp now gets to 70. Is it absolutely for sure that using a Nest is problematic here?

    Thanks for all the feedback here. Super helpful.

    Please go back and read what I posted about the Nest again. It is absolutely a problem.

    If you want remote control of the thermostat, then look at using the Honeywell Lyric wifi stat or similar, but not the Nest which uses intuitive logic that fights the logic of the boiler.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • sbnycsbnyc Posts: 5Member
    Ironman said:

    sbnyc said:

    If you want remote control of the thermostat, then look at using the Honeywell Lyric wifi stat or similar, but not the Nest which uses intuitive logic that fights the logic of the boiler.

    Got it. Will look into the Honeywell Lyric. Thx!
  • kcoppkcopp Posts: 3,411Member
    Looks like your condensate pump is either broken or the exit is frozen/ blocked.
  • sbnycsbnyc Posts: 5Member
    kcopp said:

    Looks like your condensate pump is either broken or the exit is frozen/ blocked.

    @kcopp - The weather has been pretty mild most of the winter, so I dont think anything is frozen. But thanks for confirming it is probably broken or not working correctly. Wondering - could this be from sediment in our water lines?
  • kcoppkcopp Posts: 3,411Member
    edited February 14
    Has nothing to do w/ your water... the condensate is from the boiler combustion process. Look at the 3/8" Vinyl line and see if it is pinched off. The pump looks like it wants to drain out... but cant.
  • sbnycsbnyc Posts: 5Member
    kcopp said:

    Has nothing to do w/ your water... the condensate is from the boiler combustion process. Look at the 3/8" Vinyl line and see if it is pinched off. The pump looks like it wants to drain out... but cant.

    Thx, just spoke to service guys and they are going to take a look.
  • SuperTechSuperTech Posts: 1,126Member
    @sbnyc If the air handler has an external hot water coil it should have a pipe mounted aquastat relay to bring on the fan, especially if the air handler has a lot of pipe between it and the boiler. Any HVAC technician familiar with hydro air should know how to do it. The aquastat can be wired to switch a high or low voltage circuit, depending on whether you have an old fashioned PSC fan motor or an ECM motor.
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