question about strange behaviour of home heating system

[cbrn]

Hi,

I don't know if I'm a bit off-topic, but I really hope someone can help me understand what's happening to my home heating circuit.
Circuit: a gas-burner water heater is alimenting a collector via its circulator-pump; from the collector, six "antennas" depart, each controlled by a servo-valve, and each alimenting a tube radiator; These six antennas are grouped in two "zones", each piloted by a thermostatic room sensor.
Problem 1: in this original configuration, the water flow in the radiators was VERY noisy.
Diagnosis 1: the circulator was probably regulated for an exaggerated flowrate.
Remedy 1: the circulator has been "slowed down", and the technician of the heater said that it would be better to also install a bypass on the collector.
Problem 2: by slowing down the circulator, the noise diminished, but unfortunately now with the bypass a new fact occur: when the two "zones" are opened, all OK; when one of the two zones closes, or worse when both close (temp in the rooms has been reached!), the heater emits a loud hissing noise every time it shuts off after having started for some seconds to keep its own internal primary circuit hot.
This thing is driving me crazy, since I never heard of it in any other home heating system, and the heater technicians and hydraulic men do not agree at all on which could be the cause(s).

I don't know if my explanation is clear...

Thanks in advance to anyone would help me!

Regards

 

[TBP]

Does it sound like your system is full of BBs? If so, that's likely air bubbles. Your system should be layed out such that the circ pump is on the outlet side of the boiler, pumping away from the boiler, and toward the system. Between the boiler and the pump, is where the air separator and expansion tank should located. This means the air separator is positioned at the point of lowest pressure (the expansion tank pressure rules the system) and the highest water temp - at the boiler outlet. This is where the system water is closest to the boiling point, and dissolved air will be most prone to popping out of solution. It also matters where the little make-up water pressure reducing valve is located. It should be connected to the short section of pipe between the expansion tank, and the heating system.

 

[abeltio]

agree with TBP as a likely source of noise.
make sure that all the high points are properly vented.

note that i say: all the high points... in a system you may have many more than one high point.

follow the piping... if the piping goes up and then goes down... that is a high point... sometimes called: inverted "U"

what is the water temperature? if the water temperature is near the boiling point and there are non-vented inverted U's... most likely steam will separate causing loud popping noises.

is there a pressure gage in the system? if there is air... the pressure gage will jump all over the dial

hth

saludos.
a.

 

[cbrn]

Hi,

first of all, thank you very much for your kind advices!!!
Yes, I had already thought that the problem might be trapped air, but I checked all the vent ports in the system, especially on the two highest radiators, and there was absolutely none. Knowing that some heaters dislike working with low pressure in the circuit (namely, 1.1 - 1.2 bars), I raised the water pressure to 1.4 bars. The water temperature is regulated at 55°C. Today I spent some time with the bypass valve: it helped tuning it so that it isn't too stiff to open when the circulator pump is running with all the "antennas" closed (it should be only transitory, because once all the "antennas" are closed, the heater's controller is aware of it and after a couple of minutes it stops the heater's activity, incl. the pump.
I'd say that now the hydraulic circuit seems OK.
The loud hissing noise I hear now is, strangely, entirely the fault of the heater: it is an "air-suction" noise coming from the burner chamber. As the flame power is not constant, this noise appears and disappears, making it difficult for me to understand exactly in which conditions it happens. I think I should contact the tech assistance of the heater...

Thanks again to everybody,

regards