Hi there,
Last week the central heating system starting making a loud screeching and banging noise. We traced it to the GRUNDFOS pump which we removed and replaced yesterday. After we re-opened the isolating valves on either side of the pump, we bled the pump and started the central heating system.
After about 15 seconds the pump started scavenging and getting louder. We opened one of the bleed valves on a radiator and no air or water came out – it was empty. Tried all the rads on the first floor and they were all empty.
Then we checked the HW tank and found that the motorised valve on the HW side of the system wasn’t opening (I think it’s an ‘S’ plan; we have 2 motorised valves) – after removing the motorised head you could hear the motor trying to work. We manually opened the valve and tried the HW again.
After about 10-15 seconds the same thing happened; the pump got louder and we heard hot water coming out of the expansion pipe over the header tank in the loft. We tried to drain the system thinking it might be an air lock, but when we got the boiler (an old BAXI type) we couldn’t find a drain cock. However we did find a large cube type thing on the inlet side of the boiler with a fitting underneath. Does anyonme know what this is? We didn’t want to start trying to open it in case it broke – the boiler is about 30 years old. My dad thinks there might be a filter in there or some kind of valve that could be stopping the water from filling the system? Anyone know what it is?
Then we tried draining the system from one of the rads downstairs – a bit of water came out but not much. Went and checked the header tank in the loft and it was still completely full.
There’s nothing in the header tank causing a blockage.
My suggestion is that the motorised valve has failed causing the boiler to spit water out into the expansion tank. Because the system isn’t filling properly, this has run the pump dry and knackered it. Don’t know why the system isn’t filling back up though?
Can anyone suggest what we should try next or why the system might not be filling..?
Thanks in advance, Phil
Last week the central heating system starting making a loud screeching and banging noise. We traced it to the GRUNDFOS pump which we removed and replaced yesterday. After we re-opened the isolating valves on either side of the pump, we bled the pump and started the central heating system.
After about 15 seconds the pump started scavenging and getting louder. We opened one of the bleed valves on a radiator and no air or water came out – it was empty. Tried all the rads on the first floor and they were all empty.
Then we checked the HW tank and found that the motorised valve on the HW side of the system wasn’t opening (I think it’s an ‘S’ plan; we have 2 motorised valves) – after removing the motorised head you could hear the motor trying to work. We manually opened the valve and tried the HW again.
![5.jpg](http://www.upjumpcupcake.co.uk/images/heating/5.jpg)
![6.jpg](http://www.upjumpcupcake.co.uk/images/heating/6.jpg)
After about 10-15 seconds the same thing happened; the pump got louder and we heard hot water coming out of the expansion pipe over the header tank in the loft. We tried to drain the system thinking it might be an air lock, but when we got the boiler (an old BAXI type) we couldn’t find a drain cock. However we did find a large cube type thing on the inlet side of the boiler with a fitting underneath. Does anyonme know what this is? We didn’t want to start trying to open it in case it broke – the boiler is about 30 years old. My dad thinks there might be a filter in there or some kind of valve that could be stopping the water from filling the system? Anyone know what it is?
![1.jpg](http://www.upjumpcupcake.co.uk/images/heating/1.jpg)
![2.jpg](http://www.upjumpcupcake.co.uk/images/heating/2.jpg)
![3.jpg](http://www.upjumpcupcake.co.uk/images/heating/3.jpg)
![4.jpg](http://www.upjumpcupcake.co.uk/images/heating/4.jpg)
Then we tried draining the system from one of the rads downstairs – a bit of water came out but not much. Went and checked the header tank in the loft and it was still completely full.
There’s nothing in the header tank causing a blockage.
My suggestion is that the motorised valve has failed causing the boiler to spit water out into the expansion tank. Because the system isn’t filling properly, this has run the pump dry and knackered it. Don’t know why the system isn’t filling back up though?
Can anyone suggest what we should try next or why the system might not be filling..?
Thanks in advance, Phil