Heat Pump Water Temperature goes up at night - Page 1
Forum section: electronics / repair

author: zizebra
author_rank: Contributor
timestamp: January 09, 2025, 10:09:41 pm
content: Hi AllMy heat pump has a strange problem which i am trying to figure out. I do not have ideas on how to approach the issue. Initially i thought the thermistor for the geyser was faulty so I purchased a new one. The old one simply showed water temperatures between 60 and 80 degrees. Occassionally the temperature would be ok and the heat pump would heat up water. Now with the new sensor, first day it was ok worked perfectly. Then the next day around 7pm, the temperature started creeping towards 60 when the actual water temp was around 40degrees. Switching the settings to use outgoing temperature solves the problem. Water is heated properly as per requirement. But if i use the incoming temperature, the issue resurfaces. The temperature goes up and heat pump wont heat the water as the temp will be above normal. Strangely enough, as soon day the starts when the outside warms up, the heat pump starts reading the temperature correctly and operates normally. Now iam trying to figure possible causes to determine if this is a minor issue and where i can start and diagnose or simply get a new board.

author: Poroit
author_rank: Frequent Contributor
timestamp: January 10, 2025, 06:29:20 am
content: G'day zizebra,There are lots of variations with thermistor type and resistances.Do you have any specs on the Thermistor and are you sure you replaced like for like?

author: zizebra
author_rank: Contributor
timestamp: January 10, 2025, 07:49:21 am
content: Not sure how best to answer your question but I did determine that the thermistor was 10k NTC. how the observation which is worrying me is that both the old and new seemed to be unable to provide the right measure during the night starting after around 7pm up until the next day when the sun rises. This is what is baffling me as I thought the original thermistor had given up. Now it seems there is something else on the board that is probably acting up.

author: thephil
author_rank: Regular Contributor
timestamp: January 10, 2025, 08:36:33 am
content: The first thing I would do is verifying that the reading is really the sensors fault. I.e. measure the resistance with a multimeter and get the corresponding temperature from a reference table for your sensor. Repeat a few times during normal operation and times where the reading is off. That will tell you where to look further: sensor or control board.

author: zizebra
author_rank: Contributor
timestamp: January 10, 2025, 06:03:26 pm
content: Thank you. I will check on that this evening. My mind was stuck thinking it must be the board or something else.

author: Poroit
author_rank: Frequent Contributor
timestamp: January 11, 2025, 09:23:54 am
content: Are you able to confirm that the water temperature is actually 70°C by some alternative measurement?Does your Heat Exchanger Indicate both Inlet and Outlet Water Temperature?

author: Swake
author_rank: Frequent Contributor
timestamp: January 11, 2025, 03:03:39 pm
content: I consulted my crystal ball but it refuses service due to missing crucial information.Can you share model/make of the heatpump. Some pictures of the heatpump as installed as well as pictures and model number of the temperature sensor and the place it is located on the heatpump.How do you know the temperature, does it have a display? What else is it showing? Are you certain it is showing the temperature of the sensor you changes or might it be of another sensor?Any other components such as a thermostat? Is that heatpump only for hot water or also for heating? What is the ambient temperature?

author: zizebra
author_rank: Contributor
timestamp: January 12, 2025, 04:01:51 pm
content: i can confirm the water is not 70 degrees because i have another sensor that is running off a sonoff device and i also know because water on the outlet is cold. I also know this because the heat pump has a setting which allows one to change the sensor which is used to control the heating. The sensor used is either incoming or outgoing water sensor. The heat pump is typically configured to make use of the incoming temperature sensor. When i change heat pump settings and start using outgoing water temperature, then heat pump operates normally. The outgoing reflected temperature for outgoing matches the sonoff temperature and heating of water definitely takes place.Last confirmation based on the idea by @thephil. I removed the sensor and put 10k resistor in place of the sensor. Based on this the temperature was supposed to stay in line with the static value of resistance. However the observation was that the temperature reported still went up even though there was static resistance. With this detail i went hunting for another board which solved the problem, the heat pump is working perfectly with another board. Now i am just trying to determine which component on the board that was acting up.

author: joeyyyyy
author_rank: ZeroPoster
timestamp: April 30, 2025, 08:07:37 am
content: NOTE: This message has been deleted by the forum moderator Simon for being against the forum rules and/or at the discretion of the moderator as being in the best interests of the forum community and the nature of the thread.If you believe this to be in error, please contact the moderator involved.An optional additional explanation is:

author: Swake
author_rank: Frequent Contributor
timestamp: April 30, 2025, 11:19:38 am
content: Soooo, joeyyyyy,.... Tell me how this is not an ad/spam ?

author: Seekonk
author_rank: Super Contributor
timestamp: April 30, 2025, 01:14:10 pm
content: My guess with a board problem is the voltage regulator. In the evening line voltage typically increases as load on the grid drops.I had problems with a LG washer on occasion giving a failed temp sensor error. That kept the washer from working even though we did not use any heating functions. Our basement is very cold on some winter days. I pulled out the temp sensor (10K) which read correctly upstairs and added a 150K resistor in parallel to make the machine think it was warmer. Some controls are too smart for their own good.