"Bought to replace Sunviv SZ2301. Only needed the motor/switch part due to micro switch sticking on Sunvic unit [boiler running all the time]. 20 minute to swap the unit. As stated by another reviewer Sunvic unit lasts about 2years then problems, hope the Damfoss does better. Consult an electrician if unsure about the wiring."
"I have 3 x 2 port all 4yrs old, now they have become sticky ie, program shuts down boiler still going and pump running but valve has not completely shut, switch off power supply for one min. then turn on problem sorted. Replace motor body, costly."
"I have three two-port valves in my system and have had several different makes of valve. This Danfoss HP22 has been good for the last four years but now I have a sticking valve body despite oiling the gland. The spring pressure is not enough to close it though the switch does go off. The result is that if either of the other two valves (main heating and water) causes the pump to come on water will leak past the faulty valve and heat up the radiators in that zone (the granny annexe). This means another system drain and more system preserver as well as a new valve. The actuators seem much more robust than other makes that I tried."
"These motorised valved have an integral micro switch that is prone to sticking, either in the on or off position. The actual water flow part seems trouble free so its the additional stuff that the switches operate that won't work properly. If you fit them, be prepared to replace the "motorised head " every 3 years or so."
"Had four of these professionally installed as part of a large installation. Three have failed within 2 years. The valve seems fine, it is the motorised head that stops working - but it seems you need to buy the complete assembly to replace just the head. Fortunately it is easy to replace - just held to the back plate by two screws. When working they're fine but cannot recommend them for durability. If another one fails I will definitely look for an alternative make."