Veissmass 200W High limit switch problems

Tonerlow

We have retro fitted a 200w into our 1250 sq ft split level bungalow. There is one circ pump running 2 heating zones one upstairs one downstairs. A problem occurs when one heating zone is satisfied, circ pump cuts out instantaiously to the burner. The latent heat in the coil builds up due to no overrun time on the pump. Then every so often the second zone calls for heat very quickly and the heat has not had time to dissipater form the coil. This pulls the superheated glycol over the tstat and causes F2 fault. My contrator has been unable to properly remedy this for 2 years now so i am looking for outside opinion. Thanks

pedmec

Pic of system

GGross

@Tonerlow

You are making a few assumptions here. First of all, how many total pumps are on this system? and please take pictures of your boiler room.

Tonerlow

one pump running heat to both zones, fin tube radiators. And one pump running to the hot water tank.
Will post pics when i am able

GGross

@Tonerlow

Hopefully the pics clear it up, that boiler should be piped primary/secondary, 1 pump just to fire the boiler, separate pump to fire boiler for DHW call, and at least one other pump to come on and off with your thermostat calls for heat. Off hand it sounds like a flow issue/bad piping. That boiler wants to target a supply temperature at the low loss header, it needs its own pump to make proper flow through the heat exchanger, the pump should not turn off as soon as a call for heat ends with that boiler, the boiler should satisfy its supply temp and shut off the pump itself. Running off the fixed high limit for 2 years has me concerned that the boiler will fail prematurely

Tonerlow

also of note no LLH in this set up. Yes I am also very concerned about the longevity of the appliance due to these issues. I will post pics to help you gain some more understanding of this set up

Tonerlow

Last winter we had it programmed so that the boiler pump was running continuously. This remedied the F2 fault but created another problem because during a cold snap, without DHW priority set up, the boiler pump would demand too much energy and our hot water would not be adequate. Also i disliked this setup because I could hear the glycol cycling through a manual bypass 24/7

Tonerlow

Thanks for all the insight so far

GGross

Tonerlow said:

Last winter we had it programmed so that the boiler pump was running continuously. This remedied the F2 fault but created another problem because during a cold snap, without DHW priority set up, the boiler pump would demand too much energy and our hot water would not be adequate. Also i disliked this setup because I could hear the glycol cycling through a manual bypass 24/7

The thing is, that boiler will control the primary boiler pump, and the DHW pump on priority. If it were piped primary secondary and the boiler controlled at least those two pumps, the issue would go away, P1 and P2 in this picture should both be controlled by the boiler. P3 and the zone valves can be controlled by a separate relay and thermostats. The black box is the low loss header, and though it is not required the concept that it enforces is required, we need to guarantee flow through that heat exchanger, and the pump cannot turn off before the burner, or you risk going off on that high limit. At least thats what sounds like is happening, pump turns off when thermostat satisifes, then the boiler shuts down from the flow switch (there will not be an error code for that) sometimes it just overtemps due to no flow and locks you out.

Tonerlow

yes
Ii think you have a pretty good understanding of what is going on here. when I turn down my basement thermostat and watch the boiler display, the boiler temp rises by up to 30 degrees C due to no flow. (when the call for heat ends) All that is needed to remedy it (in my opinion) is the ability for the pump to run an additional 1-2 min to move that heat energy out into the piping rather than it remaining in the coil. My contractor has not been able to find a coding condition that allows this. I also would have to ask him if the circ pump is currently boiler controlled or simply running with the tstat and zone valve as its controller

GGross

@Tonerlow

It is possible that the pump is controlled by the boiler, but when the zone valves close the pump dead heads against the valve resulting in no flow, either way if it is not piped primary/secondary, similar to the above picture it needs to be re-piped. Your plumber will not be able to fix this via coding only unless there is a bypass pipe somewhere for the pump to continue circulating.


By default the boiler runs the pump with the burner, the burner shuts down when temp is satisfied (supply temp not room temp), there is an exhaust post-purge, and the pump will shut down, there is always at least a brief delay where the burner shuts down, and then the pump turns off. If the pump is shutting down, and then the boiler temp shoots up that tells me that the boiler is either not controlling the pump, or the zone valves close creating a dead head -no-flow scenario. Just to be clear what is happening is that the burner still runs very briefly after the pump turns off (or while pump is dead heading), then the flow switch cuts out the burner, this is not latent heat leftover in the coil, if it were these boilers would always go off on limit and they do not. Personally I would consider this a dangerous condition. Your contractor needs to look outside of coding and attempting to bypass safety devices, and just pipe it correctly

Tonerlow

we do have a small bypass installed to avoid deadheading. it is a 3/8 copper line with a ball valve which needs to stay about halfway closed in order that enough fluid circulates to the upstairs during heating calls. Also kettling can be heard inside the boiler when the call for heat is satisfied. In any event I will get some pics posted so you can confirm your theories about this setup

pedmec

When was the last time you had the heat exchanger inspected. it sounds more like have a plugged heat exchanger. I say this because you said when the initial call for heat is satisfied the temperature in the boiler keeps rising. in a mod/con, which i'm assuming you have, the heat exchanger is never that hot as its always modulating on demand and by design transfers most of the heat from the flame to the boiler water as indicated by low flue gas temperatures. if its rising after shutdown you have to have something in the heat exchanger that is absorbing the heat and on shutdown it still heating the water in the heat exchanger. dead heading a mod/con will cause flashing of the boiler in the heat exchanger and you will know it when it happens because it can be a pretty scary banging noise.

Tonerlow

The plumber actually showed up today. They are going to set the circ pump up to run constant so that will pull the heat out of the coil. The small bypass should allow enough flow as it has ran this way previously. Then to enable DHW priority he is wiring a “Double throw double replay” switch which will power down the circ pump when DHW pump powers on. They are also adding an additional lockout switch on circ pump so I can manually disable it thru the summer months when there is no need for it to run. The heat exchanger has not been inspected as the unit is only 2 yrs old right now. 

@GGross Your theory seemed correct in that the boiler appears to continue firing for about 12 seconds after the call ends in the current setup. So that would be the flow sensor you speak of.  

Tonerlow

 @GGross

GGross

@Tonerlow

I might just be missing it but I do not see a relief valve in the photos. It kind of looks like he has a relief valve piped at the bottom left of the boiler, with the blowdown line going into a hole he cut in to the filling unit? (the thing that says axiom DMF150) Have you ever noticed fluid coming out of that line and going into the filling unit? I really don't like how that is done

I am curious if the plan will work, the potential issue I see here is that the boiler may still be firing as one pump is turned off, and the other pump turns on. While I still think the plumber should pipe it correctly, I think the main concern is that we do not keep cycling the boiler on its fixed high limit. Stuff like this really bothers me as it looks like you received a hack job for sure. Let me know if the plumbers plan keeps the boiler from hitting limit.

edit: I should add that what the plumber is proposing with controlling those pumps is handled by the boiler if he just wires them to the boiler like they should have been from the start, including turning the primary pump off during warm weather, it is automatic and you do not need a manual changeover switch like he proposes. He just needs to open the install manual for that boiler one time and take a look at the wiring and piping diagrams

Tonerlow

Yes the relief valve drains into the fill unit as you have spotted. I have never observed anything draining into there. It was -24 Celsius here last night and ran fine with no faults, house actually seems to be staying warmer throughout also. I think the way it is set up that the pumps will run simultaneously for a split second? As hot water pump has to activate, open coil on the relay, relay shuts down circ pump. I do not think there will any longer be periods of firing without flow with this setup? My last concern is i have reached out to the plumber (he sent one of his electricians yesterday) to suggest he does the 2 yr inspection for us pro bono to compensate for all the start up issues. I would like him to inspect the heating coil for scaling or damage due to the repeated high limit faults. 

The electrician who came yesterday also thought this set up will be the safest, as it maintains flow, as you pointed out yesterday that no flow was causing the fault as well as an unsafe condition.

My last question: Do you get paid by this site for all of the feedback? You have a very extensive knowledge and if you are offering this for free what a service to all users of this site!  

Tonerlow

@GGross I should run another situation by you. We have a 200W Veissmann at my place of work also. It is a 200K Btu model providing in floor heat to a 7200 square foot shop plumbed in 2 zones. We also have a small mechanical room built as a lean to on to this building. This slab was poured after the main shop and has no in floor piping. We do not get enough heat out of the main area into the mechanical room to keep it from freezing up (we have a pressure washer and large tank in this room )

The contractor (a different one than did my house) plumbed on a Unit heater with a fan to provide heat to this room. The problem we have encountered is that the boiler seems not to know when the small room is calling for heat and does not increase supply temp to satisfy this call. Thus the unit heater will run all day with 40C glycol cycling thru it and will never make any tangible difference in the temp of this room, let alone satisfy the tstat. This was a 3500$ addition to the heating system in that building and has proven to be basically useless. Is there not a way to have the boiler increase supply temp temporarily to blast the small room with hot air (it is at most 400 square foot area) This 200000 BTU boiler should be able to heat that room up in a matter of minutes, or am I mistaken/missing something here. I did one day turn the SHIFT up substantially to test this set up and it does indeed blow hot air when you do that, so I would assume the flow/pump/etc is all in working order.

So right now we have heat trace tape on the line for the pressure washer, and leave the 8'X8' (i think) door open which connects these structures to pull some heat in from the main building. Use a floor fan to blow a little more warm air in there when we hit our -40 C days up here in Canada

I can definitely provide pictures of this system if you think you could have any suggestions

Tonerlow

@GGross The unit has ran thru the night, no faults. -27 here this morning with -33C wind chill. The house actually seems to be staying more comfortable overall somehow. Our kitchen used to be noticeably cold as there is only one baseboard fin tube under one window in there, no output around the cabinets fridge stove etc.

Yes you have correctly identified the pressure relief and how it is piped, I have never observed any fluid transfer there nor have I heard the fill pump ever run. My wife has been home for one year with our newborn so I'm sure that fill pump has never ran or we would have heard it

The sequence for the pumps will be DHW pump on, activates relay, disables circ pump. So I think? the situation of firing without flow should be eliminated? As the circ pump cannot disable until it receives the signal from the other pump

The plumber sent his electrician on the call yesterday and he agreed this set up will be the safest as it ensures flow is always there, as you had pointed out yesterday that was the issue we were having I am quite certain. There was fire with no flow when the pump cut out and the boiler was not aware of the condition until it detected flow had stopped, by which point it had started to spike the temp.

I have asked my contractor to do the 2 year inspection on this system as a courtesy to us to compensate for all of the screwing around. Hopefully he obliges this request. I would like to know that the HX has not been damaged under the repeated fault conditions. Although it has not been 100s of faults maybe 50-60 total if I had to guess.

Our next and hopefully final issue it that the south west bedroom upstairs does not receive as much heat as the rest of the upstairs. I can only assume it is at the end of the loop and thus loses out on a few BTUs. I have closed almost all dampers upstairs in order to get more heat to this room, it does remain adequately heated but just about 4C cooler than the rest of the house. Leaving the door open also helps equalize the temps but our 1 yr old sleeps in there and so sometimes it is preferable to have his door closed. The only way I see to remedy this issue is to substitute/add a larger fin tube in this room? This is not too costly of an addition?

One day I would love to renovate the basement and switch the upstairs to in floor heat, but this is not going to be cheap and wont be happening anytime soon.

GGross

@Tonerlow


Yes it is possible for that boiler to recognize up to 3 different calls for heat, each with its own heating curve (that would control the temperature the boiler fires at)

With a set up like that, 2 temperatures, you should have a mixing valve in place to control the temperature that is being sent to the floor, you don't want to overtemp the floor, if the air handler calls and the pump for your infloor is also going, you could send really hot water to the floor. see the attached drawing from the application manual for reference, it points out the mixing valve. In that application they are using a thermostatic mixing valve, this will maintain a single setpoint temperature, or below. Ideally you would use a motorized mixing valve, which would modulate the outgoing temperature to floor to match exactly with your heating curve. The Vitodens 200 boiler is capable of controlling a Viessmann motorized mixing valve via the built in control, the only issue with that is that they can be a bit pricey

Before all that I would make sure that the boiler room area is well insulated

Tonerlow

@GGross Are you paid by this site? You have a great knowledge of these systems and I must say if you are spending this much time helping strangers for the fun of it that is quite admirable. Also did you see my comment from 10:32 and do you have any thoughts on it

Our boiler room is 2x8 walls so it is well insulated although it is drafty we do need to seal the sill gasket where it lets the wind howl in

GGross

@Tonerlow

Adding baseboard to that space should help. You may want to find a contractor that can do a heat loss calculation on the space before proceeding, that way at least you know that you have the proper amount of baseboard.

Tonerlow

@ggross what is a typical supply temp required by an air handler such as a Reznor WS23/33

GGross

@Tonerlow

I don't see the specs on the sheet for different water temperatures, generally you can send pretty much any temperature your overall capacity will just be reduced. I would say that 120 is pretty low for them, typically too low. Most of the time when they have a BTU rating shown it is based on steam temperatures, so you would need to get a model that has a listed rating quite a bit larger than the load of the space (unless it is specified as a "low temp model"). I would ask whoever you are purchasing this from for a chart that shows the expected output at different supply temperatures to be sure you are selecting the right one.

Modine has a low temperature model that I have used a few times with good results
https://www.modinehvac.com/products/unit-heaters/steam-hot-water-unit-heaters/lodronic-low-temperature-hydronic-heater-hch/

Jamie Hall

To @Tonerlow 's question -- no, we are not paid or compensated in any way, other than the pleasure of helping others.

Tonerlow

@GGross Here are the install pictures. It’s me again. I just tagged you in the other thread about vibrations. 

I am seriously getting fed up with this. Have inquired with the plumber about repiping this as you had suggested awhile back. Just never ending issues and that shouldn’t be the case with state of the art equipment like this.