Air-source heat pump low pressure problems

[greenman]

Hi
I have a Dimplex LA16MS air source heat pump which has started playing up in this latest cold snap.
It keeps on cutting out with the message 'Low pressure limit. HP waiting' and whilst sometimes it seems I can hit the Esc key to acknowledge the message and then it starts working again, on other occasions it starts up and then pretty mush straight away cuts out again.

According to the operating manual for the controller (WPM 2006 plus) the heat pump should recover automatically, but it doesnt seem to do this unless I clear the message.

Anyone any ideas as to whether I can change any settings to get over the problem or is it time to call out the professionals?

The unit is about 6 years old and has been working fine bar a couple of blown soft starts due to local electricity supply issues which, touch wood, seem to have been rectified now.

Thanks in advance for any advice

[frank]

Is your system on R407C refrigerant?

I'm not familiar with the Dimplex systems but R407C seems to trigger LP faults during cold weather. Our Daikin cassette system in the office suffers such a condition when outdoor temps drop below -5C

Some systems employ 'Cold Start' timers that bypass the LP switch.

[Bigfreeze]

Hi
I have a Dimplex LA16MS air source heat pump which has started playing up in this latest cold snap.
It keeps on cutting out with the message 'Low pressure limit. HP waiting' and whilst sometimes it seems I can hit the Esc key to acknowledge the message and then it starts working again, on other occasions it starts up and then pretty mush straight away cuts out again.

According to the operating manual for the controller (WPM 2006 plus) the heat pump should recover automatically, but it doesnt seem to do this unless I clear the message.

Anyone any ideas as to whether I can change any settings to get over the problem or is it time to call out the professionals?

The unit is about 6 years old and has been working fine bar a couple of blown soft starts due to local electricity supply issues which, touch wood, seem to have been rectified now.

Thanks in advance for any advice

Its possible that it trips on LP when defrosting. If you are getting poor flow across the evaporator (the condenser in heating) then the evap temp will drop. Alot of systems with not very sophisticated controls will us a high setting on the LP switch to prevent the evap freezing and bursting. If you have a filter on the heating water check if its getting blocked or maybe a pump is running slow. This will affect your performance in heating mode too.

[The Viking]

First things first,

It's an air source heat pump...
Have you checked that the outdoor unit's coil is clean and free, the outdoor unit's fan is running smoothly and there is no obstructions to the airflow?
There is 2 main reasons for the LP switch to be activated, either low airflow across the outdoor unit's coil or a lack of refrigerant. If you checked the above then it is time to call in a professional to recover the refrigerant and verify that the charge is correct.
After this has been eliminated we can start chase for more exotic faults.

:cool:

.

[greenman]

No, its R404A.

The temperature outside has gone well above freezing now (according to the console) and the problem is still occuring.

[greenman]

Everything looks clean inside the unit...gave the coil a light brush anyway. Fan all seems to be fine.

I have now noticed that the system seems to correct itself if I just leave it alone, but it can take some hours, by which time our hot water and heating tanks are both practically depleted of heat.

Whilst I had the unit open I noticed there was a small amount of water pooled around the the base of the coil but I assume this is from condensation?

Is it common for the refrigerant to leak out of these units and need topping up?

[chemi-cool]

Is it common for the refrigerant to leak out of these units and need topping up?

My thought as well, If the unit have lost some charge, it will not be able to perform defrost and i think that is the reason why it does not recover automatically.

Dont top up but replace the charge and check the defrost operation.

At temps near 0C there should be some ice on the evaporator.