Why Does My Hot Water Circulating Pump Bang When It Starts Up?

[Brian]

I have recently had a new boiler and circulating pump installed keeping the hot water cylinder. I have the hot water timer set to come on for an hour each morning but when the time is reached, a loud bang comes from the pump which can be heard all over the house. Can anyone please suggest what the problem is and how to cure it? If it is not a simple job, I will call the installer back to attend.

 

[John.g]

45w indicates either a very high head with a moderate flowrate or a very high flowrate with a low head, would suggest trying fixed speed 2 or CP1 (constant pressure), while you are waiting for help. Also there seems to be a balancing (gate?) valve on the cylinder coil return with the wheel head removed, if so you might try shutting this fully and then just open it 3/4 to one full turn and then maybe try the above settings.

 

[Hollinside]

Exactly the same thing in my house - we had a grundfos 25/80 pump and the same type of valve- the 3 port valve stays in its last position until it receives a signal to move. Pump turned on at same time as the pump started and it sounds like a bus crash in there! Newer wilo pump seems to start up slowly and auto adapts and the almighty crash disappeared instantly. If I turn the pump on full power no automatic adapt it can still be replicated though! Try a lower pump setting before shelling out on another valve,

 

[John.g]

Shoud have said try CP2 (not CP1) above.
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Exactly the same thing in my house - we had a grundfos 25/80 pump and the same type of valve- the 3 port valve stays in its last position until it receives a signal to move. Pump turned on at same time as the pump started and it sounds like a bus crash in there! Newer wilo pump seems to start up slowly and auto adapts and the almighty crash disappeared instantly. If I turn the pump on full power no automatic adapt it can still be replicated though! Try a lower pump setting before shelling out on another valve,

Should have asked Brian originally if he had this valve installed before renewing boiler/pump and if so was there still banging, also if he has a 8M pump now installed, IMO 20/25W should reflect a reasonable pump setting selection. I too have 6M Wilo (yonis pico) and on any of its PP or CP settlings it ramps up slowly on every retart and takes - 5/6 seconds to reach its setpoint, I would have thought that the Grundfos would behave in a similar fashion?.

 

[Brian]

John, Everything except my cylinder has just been renewed together with my boiler. I never had any banging before. Not sure if the pump is an 8M.

 

[John.g]

John, Everything except my cylinder has just been renewed together with my boiler. I never had any banging before. Not sure if the pump is an 8M.

OK then, all I can say is that 45W is IMO indicative of excess flow/pressure and reducing this may at least alleviate the problem until you get your installer back, let us know the outcome.

 

[Brian]

Update. I have had the installer attend. He has made some simple adjustments to the pump and now, all is well. Thank you all for trying to help.

 

[John.g]

Good to hear that, if you don't mind you might post the present pump power and if possible the pump setting.

 

[Brian]

Hello John. I am not really sure about the settings. All I can say is that there are two buttons. The one on the left is set to Auto and the one on the right which has a Moon/Sun symbol, is on the lowest setting. The dial reads 14W when it first comes on, but varies as the heat goes through. Hope that makes sense. Brian