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Andrew Smith
Andrew Smith, HVAC Technician
Category: HVAC
Satisfied Customers: 3612
Experience:  Heating and Controls engineer
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I have two Danfoss HPA2 two port motorised valves on out oil

Customer Question

I have two Danfoss HPA2 two port motorised valves on out oil fired ch system. Suddenly one (or both - hard to tell) has started to make a continuous irritating humming type noise, whether or not the heating is in operation. The noise stops as soon as I switch off the power but starts again as soon as it is switched back on. What's the problem and the solution please?
Submitted: 2 years ago.
Category: HVAC
Expert:  Andrew Smith replied 2 years ago.
***** ***** : A 2 port valve should be either open or closed.
***** ***** : Can you try the hw seperately first and see if it creates the noise
***** ***** : Then try again with heating only to narrow it down
***** ***** : Can you tell me if the pump is running as soon as you turn the power on?
***** ***** : Are the levers on the valve tight or slack when the power is off?
JACUSTOMER-3ncntrr1- :

The noise is there all the time the power is on, whether or not the heating or hot water are on. I believe the pump is running as soon as I turn the power on - difficult to be sure as the pump is in the boiler casing out in the garage and the switch is in the airing cupboard! The levers are tight when the power is off.

***** ***** : Ok, turn the power back on but leave the heating and hot water off at the programmer and let me know whether the valves are tight or slack?
JACUSTOMER-3ncntrr1- :

Still tight

***** ***** : If the pump is running when the valves are shut then it looks like one of the valves is telling the pump to run
***** ***** : IS the boiler running also?
JACUSTOMER-3ncntrr1- :

The levers are in the same position whether the heating/hw is on or off. Is this right?

***** ***** : The levers should be slack when the hot water and heating is on, but tight when off
JACUSTOMER-3ncntrr1- :

I've checked that and they are slack when heating/hw on and tight when off but should their position change when the heating/hw goes on or off? They are in the same position in both cases.

***** ***** : If you turn the hot water and heating on they they should be slack, but if you just turn the heating off then one should stay slack (the hot water one) and the heating one should go stiff as it has shut
JACUSTOMER-3ncntrr1- :

But their position remains the same?

***** ***** : Are you saying you can't see moving?
***** ***** : it doesn't move so you can see it, it moves internally and the lever gets slack when open
JACUSTOMER-3ncntrr1- :

So, what next?

***** ***** : So they do open and close as they should? I am not sure from your last answer
JACUSTOMER-3ncntrr1- :

Yes they do

***** ***** : ok, the controls appear to be woprking, can you open one at a time and see if they click when fully open?
***** ***** : It is this click that fires the pump and boiler
JACUSTOMER-3ncntrr1- :

Do you mean with heating/hw programmed as off and force the lever?

***** ***** : when you turn the power back on is the pump still running but the valves are shut?
JACUSTOMER-3ncntrr1- :

Sorry, you didn't clarify your previous question - Should I have the heating/hw off and open the controls by forcing the levers to see if they click?

***** ***** : If you can turn on one at a time and get to the valve before it fully opens you should hear the click, the hw one should be simple as you can turn down the cylinde stat to keep it off until you reach the airing cupboard.
***** ***** : Did you say the pump was still running when the valve were shut and the power was on?
JACUSTOMER-3ncntrr1- :

The noise which was the reason for my original query has now stopped but as far as I'm aware I haven't done anything which would have remedied it. Any idea what the cause of it might have been?

***** ***** : If the pump is running (controlled by the valve) but the valve is not open then it will whistle as it is trying to push the valve open when it is shut.
JACUSTOMER-3ncntrr1- :

Thanks for your help

Andrew Smith, HVAC Technician
Category: HVAC
Satisfied Customers: 3612
Experience: Heating and Controls engineer
Andrew Smith and other HVAC Specialists are ready to help you
Customer: replied 2 years ago.

The noise has returned. The heating & hw are now running on the programmer and the levers on the valves are tight. The pipes are cold so it seems that hot water is not circulating. Could this be because the valves are stuck? What's the solution?

Expert:  Andrew Smith replied 2 years ago.
If the valves do not open then the water has nowhere to go.
You should ccheck there is power going to the valves and work your way back to the programmer
Customer: replied 2 years ago.

The pump is still running when the valves are set to off

Expert:  Andrew Smith replied 2 years ago.
One of the microswitches in the one of the valves is sticking.
You will need an electrician to sort this unless you have a multimeter?

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