WARNING: This is a long post 
Trying to get to the bottom of this problem in my Dad's house. It's a well established system installed for at least 25 years without modification.
Boiler is sited downstairs with circulating pump, motorized valve and HW cylinder in an airing cupboard on the first floor.
Seemed to operate AOK until recently. Air was entering the system, boiler started making banging noises when it shut down and the boiler started cycling (due to overheating?). There was also the sound of rushing water through the pipework to the boiler when the circulating pump started and also when the pump shut down.
On investigation, the cold feed was almost totally blocked with rust as it enters the system. Water was pumping over through the vent pipe.
The cold feed has been thoroughly cleared and other pipework in the airing cupboard dismantled and checked for blockages. System has been drained refilled with cleaning solution and left for about 3 weeks, drained again and refilled with inhibitor and silencer.
The power head on the 3 port valve appeared to be sticking, so has been replaced.
System now operates much more efficiently but strange things are still happening:
- you can still hear the sound of water rushing into the boiler when the pump starts or stops. Boiler still bangs on shutdown.
- If you watch the F+E cistern, the water level rises as the water heats up (as expected). When the pump stops, the water level drops quite rapidly and water is pumped over through the vent shortly afterwards.
-when only the central heating is operating, the return pipe from the HWSC gets hot! HW flow pipework remains cold.
Did further investigation today. The primary flow pipe in the airing cupboard (which rises up the wall, connects to the vent pipe via an air separator, then tees off to the cold feed and to the circulating pump and then enters the 3 port valve) takes a long time to heat up after the boiler has ignited. Radiators start to get hot before this pipe is luke warm.
So, it seems to me that the pipework that connects to the 3 port valve (and the vent, cold feed and pump) is actually the return!?
After this long-winded explanation (sorry!) my question is that if the return pipework is plumbed as described, would this cause problems similar to my symptoms, or could my problem simply be an air-lock in the pipework?
Any other suggestions?
Trying to get to the bottom of this problem in my Dad's house. It's a well established system installed for at least 25 years without modification.
Boiler is sited downstairs with circulating pump, motorized valve and HW cylinder in an airing cupboard on the first floor.
Seemed to operate AOK until recently. Air was entering the system, boiler started making banging noises when it shut down and the boiler started cycling (due to overheating?). There was also the sound of rushing water through the pipework to the boiler when the circulating pump started and also when the pump shut down.
On investigation, the cold feed was almost totally blocked with rust as it enters the system. Water was pumping over through the vent pipe.
The cold feed has been thoroughly cleared and other pipework in the airing cupboard dismantled and checked for blockages. System has been drained refilled with cleaning solution and left for about 3 weeks, drained again and refilled with inhibitor and silencer.
The power head on the 3 port valve appeared to be sticking, so has been replaced.
System now operates much more efficiently but strange things are still happening:
- you can still hear the sound of water rushing into the boiler when the pump starts or stops. Boiler still bangs on shutdown.
- If you watch the F+E cistern, the water level rises as the water heats up (as expected). When the pump stops, the water level drops quite rapidly and water is pumped over through the vent shortly afterwards.
-when only the central heating is operating, the return pipe from the HWSC gets hot! HW flow pipework remains cold.
Did further investigation today. The primary flow pipe in the airing cupboard (which rises up the wall, connects to the vent pipe via an air separator, then tees off to the cold feed and to the circulating pump and then enters the 3 port valve) takes a long time to heat up after the boiler has ignited. Radiators start to get hot before this pipe is luke warm.
So, it seems to me that the pipework that connects to the 3 port valve (and the vent, cold feed and pump) is actually the return!?
After this long-winded explanation (sorry!) my question is that if the return pipework is plumbed as described, would this cause problems similar to my symptoms, or could my problem simply be an air-lock in the pipework?
Any other suggestions?
