I installed a Greenstar cdi 40 to heat a polyplumb suspended underfloor heating system in a 4 storey house. I'm using a manifold on each floor, each supplying 2/3/4 circuits per floor. The primary circuit is fed by a 15-60 130 modulating pump, and the each of the manifolds are powered by a 25-60 130 pump.
When starting the system from cold, the boiler tries to heat the water, but the temperature displayed rises quickly, from say 20 to 25 degrees, in 10 seconds. At that point the gradient limit kicks in, and the boiler waits 2 minutes before trying again. So ultimately the boiler can never remain on long enough to effectively heat all the water throughout all the circuits. I can get one circuit up to speed if I wait long enough, but when adding the next circuit, the cold water triggers the gradient limit when it reaches the boiler. Even when it has made progress up to 40 degrees, say, it continues to heat too quickly, activating the 2 min shut off.
This occurs with all valves open and all manifold pumps at maximum setting, with the manifold thermostats demand as high a heat as possible, in an attempt to get the flow rate as high as possible.
I have noticed that in the bottom floor of the house , the flow rate is tiny compared to the rest of the house. I have jetted all the circuits, and good flow rates are found - no sign of debris in the underfloor circuits at least. All air has been removed carefully.
Am i hitting the gradient liit because my flow rate is too low? What can I do to improve the rate? Is my system demand simply too low for the boiler? I can get the upstairs flow rates up to 10+ litres per minute, per floor. Only the bottom floor has a poor flow rate. Surely that would be enough to stop the boiler from heating up too quickly?
I am lost. and cold. please help.
When starting the system from cold, the boiler tries to heat the water, but the temperature displayed rises quickly, from say 20 to 25 degrees, in 10 seconds. At that point the gradient limit kicks in, and the boiler waits 2 minutes before trying again. So ultimately the boiler can never remain on long enough to effectively heat all the water throughout all the circuits. I can get one circuit up to speed if I wait long enough, but when adding the next circuit, the cold water triggers the gradient limit when it reaches the boiler. Even when it has made progress up to 40 degrees, say, it continues to heat too quickly, activating the 2 min shut off.
This occurs with all valves open and all manifold pumps at maximum setting, with the manifold thermostats demand as high a heat as possible, in an attempt to get the flow rate as high as possible.
I have noticed that in the bottom floor of the house , the flow rate is tiny compared to the rest of the house. I have jetted all the circuits, and good flow rates are found - no sign of debris in the underfloor circuits at least. All air has been removed carefully.
Am i hitting the gradient liit because my flow rate is too low? What can I do to improve the rate? Is my system demand simply too low for the boiler? I can get the upstairs flow rates up to 10+ litres per minute, per floor. Only the bottom floor has a poor flow rate. Surely that would be enough to stop the boiler from heating up too quickly?
I am lost. and cold. please help.
