Problems with UFH

[lup31337]

I got an issue with the UFH and hopefully someone can help me out as I see there are a lot of knowledgeable people here.
Quick brief about the situation: House with 2 floors, UHF everywhere (no radiators, not even in bathrooms), 24 kw gas boiler. Each floor has its own panel with circulation pump, actuators etc. Each room has its own thermostat which controls the circuit of that particular room.
The problem: Recently, I noticed that I cannot get higher than 20 C even though the thermostat is set to 22 C. Ground floor heats better than upper floor for some reason. It sometimes reaches 22 deg, but upper floor never above 20 deg.
Has it worked before? Yes! I have set the temperature even at 23 with no problems.
I try to think what exactly triggered this and the only thing that comes to mind is that I increased the pressure on the boiler. It was sitting at 0.9 bar, and I thought it was a bit too low and probably will give an error soon. So, I increased it to 1.6 bar. I don't know if this was the cause of the problem. I reduced the pressure to 1.2 with no improvement.
The mixing valve is set at maximum (50 C) and the boiler water temp is set at 50 C as well. Before the problem started it was set at 45 C and 45 C. All the actuators are open, since the temperature on the thermostat is not met and the boiler starts for 3-4 minutes till it reaches 56 C and stops for 7-6 minutes. Cycle repeats.
In the panel with the pipework the large pipe which goes into the mixing valve is hot. Mixing valve around that pipe is also hot, rest of mixing valve is just warm to the touch. The pump and whatever pipe that comes after the pump is lukewarm. Seems like the heat stops in the mixing valve.
Something which may be important. As I was inspecting the pipework downstairs, since it was a hot day outside, all of the actuators closed up and the pump shut down. As I touched the pump and the pipes, they were beginning to get hot. I don't understand why this would happen.
The only thing I tried to do is to reduce the flow of each circuit and reduce the pump speed. Pump is set to constant pressure and the dial was just above mid-way. I set it just below mid-way. Not much improvement. The flow reduction I made just before I'm writing this. Do I need to wait more to see some improvement? The pipes are still lukewarm.
Posting a pic with the setup. Pic was taken before I made the flow reduction. Any advice is much appreciated. Thanks!

 

[Johntheo5]

A mixing valve (TMV) requires ~ 10C difference between the HW (boiler flow) temperature and the mixed flow temperature, can you increase the boiler flow temp to 60C and reduce the TMV temperature to 50C (or 45C), also note and post the 10 flow meter readings after doing this, what are they reading now?.
The reason the boiler is tripping at 56C is because the heat load from the UFH is less than the boilers minimum output and the flow temp is exceeding the target temp by +5C and tripping the burner.
What make/model boiler?.

 

[lup31337]

Sorry if I don't get the exact technical terms right.
The boiler is a Buderus logamax plus gb072-24k v2. I set the boiler flow to 60C and the TMV to 45C as instructed. Indeed the boiler didn't shut down. Kept it at 60, drop to 58 and repeat. Saw some swings to 64 and to 56 as well. Regardless, the flame stayed on.
I do have a thermal imaging camera and made a measurement upstairs. The flow pipe that goes into the TMV measures 48C and if I measure the pipes which go to the rooms, they measure 33-34 C. Looks promising.

However, isn't 60C too high? As far as I know, for condensation gas boilers, temperatures shouldn't exceed 55-57 C to maintain efficiency.

 

[Johntheo5]

No, 60C is fine because the temperature of the boiler return is the same as the UFH return temperature which should be ~ 38ish or even less= excellent condensing, can you measure the manifold top copper (flow) pipe temperature and measure the manifold bottom copper (return) pipe with the thermal gun but wrap a bit of black insulation tape around each pipe before taking those temperatures otherwise you will get very inaccurate readings. Also add the 10 flowmeter readings and post them and also post the 10 individual flow rates.

 

[lup31337]

It's funny the black tape made like a 2 degree difference when reading. So, the flow pipe is 32.2 and the return is 30.2

 

[lup31337]

Flowmeters starting from the copper flow pipe: 4.5 , 5 , 4 , 4.5 , 2.5 , Closed , Closed , 2 , 3 L/min
The temperatures and flow ratings are for upstairs. Downstairs I didn't measured as almost all the actuators are closed. However, the copper pipe is noticeably hotter than upstairs

 

[Johntheo5]

That makes little sense that the flow temperature should be so low with a boiler temp of 60C and a mixed flow temp set to 48C, especially if the boiler is actually firing continuously. Those numbers you posted mathematically give a UFH output of 3.56kw, doubtfully IMO if your boiler can modulate low enough to give that very low output, I would have expected a flow temp of ~ 48C with a return of ~ 40C giving a UFH output of ~ 14.2kw.

 

[lup31337]

The TMV is set to 45 and I measured again and it's 35C flow and 33C return

 

[lup31337]

The mixing unit has a bypass valve. As I played with it, it has 15 turns to fully open. Right now is at 3 turns open. Should I close it completely?

 

[Johntheo5]

Good Morning,

No, not just now, that by pass is to control the flowrate and return temperature to the boiler to ensure the boiler flow/return dT isn't too high, I'll explain it later.

Your system doesn't have a conventional TMV, it conrols the volume of hot water that mixes with the manifold return flow to give the required mixed flow temperature, the (mixed) manifold flow temperature is sensed by a liquid filled capillary tube, the end of which should be inserted in a pocket in the flow manifold, can you see where this is, can't see it properly in the photo, the control valve should be spring loaded to be fully open when the capillary senses lower temperatures than the actuator control knob setting, as the manifold temperature increases then the capillary tube liquid expands and the actuator puses on a pin to shut/partially shut the hot water supply. If you are happy that you can remove the actuator only then check that you can push that pin in, probably around 5/10mm or so, it should then spring return to the fully open position. If the capillary tube had/has lost its liquid charge then valve should open fully with possible overheat problems

Before checking that pin position, you might run the 2 floors UFH, then feel the RH pipe underneath the control knob actuator (upper floor), this pipe should be at the boiler flow temperature, compare it with the same pipe on the lower floor UFH system.

Also note the flow/return temperatures on the lower floor with the thermal camera.

 

[Johntheo5]

Re boiler UFH & boiler flow/return temperatures.
Its quite common to run the boiler at say 65C flow temperature (for HW cylinder heating etc) but to only require a UFH flow temp of 40C.
A 10kw UFH system might run with flow/return temps of 40C/33C requiring a flowrate of 17.9LPM but only 4.34LPM of this will return to the boiler resulting in a boiler flow/return dT of (65-33), 32C which will trip most modern boiler burners, so some hot water from the boiler flow must be bypassed to mix with the return water to increase the return temperature and reduce the dT to say 20C, boiler return 45C.

 

[lup31337]

The temperature sensor for the TMV is not inserted in the flow manifold, it's actually soldered to it by design. I attached I picture from the manual. I'm not conformable in removing the TMV temperature dial because it brushes against the wall and there is no room. I doubt that the pin is clogged or something. The whole system is basically brand new. This is the second winter I used it.
I also measured the pipe you mentioned. Attached a picture to confirm that we are talking about the same thing. It's 54C downstairs and 52C upstairs. Boiler is set at 60C

 

[Johntheo5]

OK, that's fine, can you now measure the manifold flow&return temperatures and the individual flow meter readings on the lower floor UFH.
You might also carefully measure its bypass valve turns open.

Do the Wilo? manifold pumps give any info re head or power in watts etc?.

 

[lup31337]

The pump is 37W nominal power, 800-4250 rpm, 3.3 m3/h max volume flow

Upstairs only one circuit demanding heat, 42C in and 38 out and downstairs everything was closed. So I turned up all thermostats and waited like 10 mins.
Here's the data:

Downstairs: 35C in and 32C Out
Flowmeters: 3 , 3 , 4 , 4.5 , 4.5 , 5 , 5

Upstairs: 36C in and 34C out
Flowmeters: 5 , 5 , 4 , 4.5 , 5 , 2 , 2 , 2 , 2 , 3

I'm guessing all circuits are more or less equally in length. Bedrooms all have 2 circuits, bathrooms have only one. Living room is larger and it has 5 circuits.

 

[Johntheo5]

That gives 6.06kw d/stairs with UFH flowrate of 29LPM @ 35C/32C with a manifold recirc of 25.01LPM at 32C mixing with 3.95LPM of HW at 54C.
That gives 4.81kw u/stairs with UFH flowrate of 34.5LPM @ 36C/34C with a manifold recirc of 30.64LPM at 34C mixing with 3.83LPM of HW at 52C.

Maybe try playing around with the recirc, you have nothing to loose.

You have virtually uncontrolled recirc which I suppose isnt that surprising with that form of mixing control, have you checked the opening turns of the d/stairs UFH.