Still cycling at 8 mins on 20 seconds off with room stats at 25 degrees. Water outlet (flow temp I assume) is up a couple of degrees but the outside temp has also dropped tonight. 

Posted by: @craig1980

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Still cycling at 8 mins on 20 seconds off with room stats at 25 degrees. Water outlet (flow temp I assume) is up a couple of degrees but the outside temp has also dropped tonight. 

Hi Craig,

To try to find the root cause of the problem, it is necessary to observe how your system is actually operating, and compare this against how we think the system should be operating.

Below are a few checks and observations to make.

Carefully time how long the system is 'on' and how long the system if 'off', ideally to the nearest second. We can then see if there is any variations.

Record the changes in the readings displayed on the controller for LWT, outdoor temperature, and any other temperature and flow readings that are available. Pay particular attention to changes from just before the heat pump stops, during the 20 second shutdown period, and after the heat pump restarts.

I'll do that today and report back. Thanks 

@craig1980

I have attached a copy of a manual which details all the various parameter settings, which are listed from page 24 onwards.

I would suggest that you go through your system and make a note of all the values.

I have my doubts over this section. 

Could this be set incorrectly? 

Its set the same for this and external thermostat application #1 (floor) and #2 (FCU).

I have no UFH so is the "floor" part irrelevant or have the set the zone 1 and 2 up as "floor" and "FCU" respectively? 

I've also just changed the 2041 Heating water law for auto mode to WL2-FCU from WL1-Floor. Is that the right thing to do as I don't have UFH? 

@craig1980

My idea was to first gather the information, then give it a close dose of inspection, and then try to decide what needs to be changed.

@derek-m no problems, it's just something I'd seen before but wasn't sure if it was correct.

@craig1980

Based upon normal operation, I would expect your system to perform in the following manner when in WC mode.

The outdoor air temperature sensor measures the ambient air temperature and conveys this reading to the controller. The controller calculates the required LWT. If either of the room thermostats are calling for heat, and the actual LWT is below the calculated value, by a specified margin, then the heat pump will start operation.

When the actual LWT exceeds the calculated value, by a specified margin, the heat pump will stop operation. When the actual LWT falls below the calculated value, plus the specified margin, the heat pump should restart. This process will probably continue during milder ambient temperatures.

What values did you record during the monitoring process?

@derek-m I'm just doing the monitoring now. 

Where would I find the LWT? I'm assuming that's leaving water temp? I have my thermometer now 

Posted by: @craig1980

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@derek-m I'm just doing the monitoring now. 

Where would I find the LWT? I'm assuming that's leaving water temp? I have my thermometer now 

The LWT is what is labelled Current Water Outlet on the 'normal' display on the controller.

I assume that your heat pump is still switching back on after only 20 seconds?

The objective of the testing, is to see what is happening to the various temperatures around your heat, as it stops and then restarts. Since the heat pump should not normally restart after only 20 seconds shutdown, something must be causing it to do so.

Images of all figures and settings on the field settings manual. I hope it makes sense?

It is on for exactly 7 mins 58 second and off for exactly 20 seconds. 

Water outlet 24.8 turns off 24.8 turns on at 21.5 indoor temp on wired remote but 18.5 on room stats confirmed by independent stats. Climbs to 27.2 at the middle of the cycle and drops back to 24.8 by the end. 

Just checked flow and return temps on rad closest to UVC and it's 25.2 -22.6