@jamespa Apologies I did know that but I seem to have replied to the wrong post
No need apologise, anything you can tell us about thermo off would be welcome. Personally I would switch it off and use features accessible from the UI to control cycling but I don't have the past experience of the system behaviour that @trebor12345 has.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
@jamespa I’ve re read through the instructions a I can’t see anything in the DIP switch settings relating to Thermo off or hysteresis. My system doesn’t require any DIP switch changes to alter the config. Is your installer referring to the setting that turns the heating completely off (Thermo off in Hitachi speak)? There is a setting that allows you to set an on/off temp with hysteresis.
Also looking at your controller setting you’ve got your pump speeds set to fixed rather than automatic delta T. I run fixed 100% for DHW as that’s what it needs in my system and auto for heating as that maintains the delta between flow and return much better than fixed.
The Thermo Off (not Thermal Off) only relates to the latest SW installed by Hitachi. To change the Thermo Off setting you have to go into the control board on the indoor unit and flip a DIL switch.
I suspect it will not work with older versions of SW.
2024 build bungalow
Southern england 179 m2 High level of insulation Underfloor heating All 12 circuits are fully open all the time 1 thermostat in family room 7KW heat pump 50 litre buffer tank (4 port)
3.6KW solar panels Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)
JamesPa You will be please to know that this afternoon WE made the DIL switch change to give us a 2C Thermo OFF time. The change was easy, but stressful.
2024 build bungalow
Southern england 179 m2 High level of insulation Underfloor heating All 12 circuits are fully open all the time 1 thermostat in family room 7KW heat pump 50 litre buffer tank (4 port)
3.6KW solar panels Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)
JamesPa You will be please to know that this afternoon WE made the DIL switch change to give us a 2C Thermo OFF time. The change was easy, but stressful.
Congratulations.
I know myself how nerve racking it is the first time you take the top off of something like this. I added the 'cooling coding plug' (a 4k resistor for which Vaillant charge £450*) to my Vaillant during the summer. About a day later I suffered from a series of apparently unrelated errors traced eventually to... the mesh filter being blocked - doubtless disturbed by switching the heat pump on after it had been off for a couple of months.
There is nothing holding you back now, you might even end up turning Thermo off off, or back to 4C, who knows!
* fortunately they also sell the exact same plug, under a different part number, to code for LPG in their boilers. The charge for that - £10
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
JamesPa You will be please to know that this afternoon WE made the DIL switch change to give us a 2C Thermo OFF time. The change was easy, but stressful.
2024 build bungalow
Southern england 179 m2 High level of insulation Underfloor heating All 12 circuits are fully open all the time 1 thermostat in family room 7KW heat pump 50 litre buffer tank (4 port)
3.6KW solar panels Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)
2024 build bungalow
Southern england 179 m2 High level of insulation Underfloor heating All 12 circuits are fully open all the time 1 thermostat in family room 7KW heat pump 50 litre buffer tank (4 port)
3.6KW solar panels Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)
JamesPa Have you seen anything in the manual about how the defrost cycle works when there is: a power cut, thermal off, demand off, HP start up, etc?
No.
Obviously it cant do anything at all when there is a power cut! Otherwise I would hope it prioritizes defrost over absolutely everything else. With your slab and unless you have a power cut lasting days there is going to be a plentiful reserve of heat to 'power' defrost when it decides to do it.
It is (apparently) possible for heat pumps to enter a doom loop whereby they cant defrost themselves. Sofaik this occurs if there is inadequate accessible energy in the house due to low system volume/zones shut off/low water temperature. I'm not sure what the recommended treatment is in these cases. If the primary has glycol in then it will still also have water in it, if the primary has antifreeze valves it should have drained. I would imagine the options are (a) wait until it warms up or (b) manually defrost using a hair drier or similar.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
The outside temperature has tonight fallen to around 0C and I am now in trouble with defrosts.
I am seeing just prior to the defrost, an evaporator of -25C. At this temperature the heat pump is really iced up and I believe the ice is touching the fan. The heat pump in this iced condition does make a rattling noise.
The defrost occurs every 45 minutes and the defrost does clear the evaporator of ice.
In the below UI image you can see that the frequency of the compressor rises prior to the defrost.
The temperature of the refrigerant also varies (HPTg).
This image also shows how the evaporator temperature drops over the 5 minute intervals.
Also the heat output to the house appears to drop.
The weight of the R32 was checked during a service visit in the summer.
I don’t fully understand the defrost algorithm, but at an outside temperature of around 0C I am sure I should not be seeing-25c on the evaporator.
2024 build bungalow
Southern england 179 m2 High level of insulation Underfloor heating All 12 circuits are fully open all the time 1 thermostat in family room 7KW heat pump 50 litre buffer tank (4 port)
3.6KW solar panels Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)
The outside temperature has tonight fallen to around 0C and I am now in trouble with defrosts.
I am seeing just prior to the defrost, an evaporator of -25C. At this temperature the heat pump is really iced up and I believe the ice is touching the fan. The heat pump in this iced condition does make a rattling noise.
The defrost occurs every 45 minutes and the defrost does clear the evaporator of ice.
In the below UI image you can see that the frequency of the compressor rises prior to the defrost.
The temperature of the refrigerant also varies (HPTg).
This image also shows how the evaporator temperature drops over the 5 minute intervals.
Also the heat output to the house appears to drop.
The weight of the R32 was checked during a service visit in the summer.
I don’t fully understand the defrost algorithm, but at an outside temperature of around 0C I am sure I should not be seeing-25c on the evaporator.
Any thoughts would be appreciated.
Currently 2° here. I’ll try and get some defrost numbers to compare
I can't comment on the defrost algorithm or numbers.
If the heat pump is not recovering temperature after defrost, I would turn off night shift. Because this limits the compressor modulation, it restricts the ability of the heat pump to recover quickly. When defrost is occurring frequently this can make a big difference to the average output. I see this behaviour with my own heat pump the ft of which cools by about 5C if low noise mode is on and it's defrosting frequently.
This post was modified 1 month ago 3 times by JamesPa
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
I can't comment on the defrost algorithm or numbers.
If the heat pump is not recovering temperature after defrost, I would turn off night shift. Because this limits the compressor modulation, it restricts the ability of the heat pump to recover quickly. When defrost is occurring frequently this can make a big difference to the average output. I see this behaviour with my own heat pump the ft of which cools by about 5C if low noise mode is on and it's defrosting frequently.
2024 build bungalow
Southern england 179 m2 High level of insulation Underfloor heating All 12 circuits are fully open all the time 1 thermostat in family room 7KW heat pump 50 litre buffer tank (4 port)
3.6KW solar panels Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)
