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JamesI, Developer
Category: HVAC
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Experience:  I have a portfolio of renovated houses, including DIY projects from installing bathrooms and new heating systems to rewiring.
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When I press the heating boost button on my Danfoss FP751 Si

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When I press the heating boost button on my Danfoss FP751 Si controller the boiler does not start but if I press the hot water button it does
JA: Just to clarify, what's the make and model of the appliance? And has it done this before?
Customer: danfoss SP715Si the boiler is an outdoor grant model I think never done it before
JA: Do you plan on doing the work yourself?
Customer: yes
JA: Anything else we should know to help you best?
Customer: I have just fitted this new controller and a new actuator
Customer: replied 4 months ago.
I asked tis question and got an estimated reply time of 8 mins I have now been waiting 40 mins when can I expect a reply

Hi, thank you for choosing Just Answer, my name is ***** ***** I will help with your query today.

Sorry for the delay in responding, average response takes less than 10 minutes but in some cases it can take hours.

When you press the boost button on the timer, does the light come on, even though the boiler doesnt start, and do you hear the relay click?

Customer: replied 4 months ago.
which relay are you asking about

There are relays inside the controller which open and close as hot water or heating is required, that is what causes the clicking noise.

Customer: replied 4 months ago.
hear a click when I press the button and the light comes on

Its likely that the relay is activating but not making contact, you can test this by removing continuity across the terminals for CH.

Once you confirm when the relay is activated its open circuit its a new timer, as these Danfoss units can be repaired, however if it is closed circuit when the boost button is pressed you need to then look at what else is in series eg a secondary thermostat or valve actuator.

Customer: replied 4 months ago.
looks as if it might have been a faulty actuator thanks for your help

No problem

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