Flow temperature up and down like a yo-yo - Air Source Heat Pumps (ASHPs)

RE: Flow temperature up and down like a yo-yo

zubadanwoes — Thu, 07 Dec 2023 13:18:10 +0000

I forgot to mention, when you are checking your air charge pressure, your water side needs to be decharged ie no pressure, usually bleeding a radiator for ten seconds will do that job, you just need a bucket or pan handy.

RE: Flow temperature up and down like a yo-yo

zubadanwoes — Tue, 05 Dec 2023 19:34:52 +0000

@greekgoddj Hello , I am not a plumber just a DIY'er, so any advice is without warranty. Have you checked your exspansion vessel for pre-charge pressure, it should be around 0.3 bar Higher than your cold fill pressure, and if it is holding water on the air side? My ASHP was aggressivley cycling on for 5 minutes, off for two, all the time it was on. I went around the house's with the pump's and system balance but after a year I checked my vessel and the diaphragam had burst , so I got blue coolant come out of the schradder valve. First hook your valve up to a bike/foot pump with a pressure gauge to see what the pre charge is, then you can remove the pump and just touch the middle of the valve for half a second to see if you get water out of the air side.

Hope you get sorted.

RE: Flow temperature up and down like a yo-yo

greekgoddj — Thu, 30 Nov 2023 09:27:20 +0000

@derek-m No update yet... Still (2 weeks now) waiting for Mitsubishi to send the replacement circulation pump first. Will for sure update this thread when I have an update.

RE: Flow temperature up and down like a yo-yo

Derek M — Mon, 27 Nov 2023 14:00:09 +0000

@glpinxit yup, that is more of less like what mine looked like last year.. so clearly something has gone wrong at the moment. I am very much looking to get it back into health! :)

Have you resolved your problem? Feedback is always welcome.

RE: Flow temperature up and down like a yo-yo

HarriUp — Mon, 27 Nov 2023 11:11:17 +0000

Have you tried lowering the WC curve to see if that has an effect?

The pump is stopping because the flow temperature is rising to its desired limit - as the return is only a couple of degrees below the flow this is happening very quickly. If you reduce the target the heat pump won't put as much heat into the exchange unit and so the water will heat up leww quickly, and even if it does continue to cycle it should be less frequent.

With a higher flow rate from a new circulation pump then that flow should be able to take the heat out of exchanger with a lower rise in temp. Your dT is quite narrow, usually slowing the pump speed creates a greater dT, but perhaps returning to a faster speed will get your system back in balance - as currently the pumps through the UFH won't have slowed to allow more heat to be given up and reduce the return temp.

RE: Flow temperature up and down like a yo-yo

greekgoddj — Sun, 26 Nov 2023 16:35:27 +0000

@glpinxit yup, that is more of less like what mine looked like last year.. so clearly something has gone wrong at the moment. I am very much looking to get it back into health! :)

RE: Flow temperature up and down like a yo-yo

glpinxit — Sun, 26 Nov 2023 14:45:28 +0000

@greekgoddj yours is like our Ecodan 11.2 looked like a year ago (but less regular). This year I've turned up the two room-stats (upstairs and down) to 2C over the day/evening target on our all-radiator system and turned all the TRVs to max. Now I'm tweaking the w/c settings ever downward. COP has improved from 3.0ish to over 4 most days and the house is a little on the warm side. Here is this morning at 4C OAT- not always quite so flat as there are occasional defrosts:

5218

RE: Flow temperature up and down like a yo-yo

greekgoddj — Sun, 26 Nov 2023 11:47:52 +0000

@sunandair Yup, I wait for the new pump.. then see if that helps the flow rate. If not then a clean of the system. By that point the flow rate should be right and that will be the moment of truth on whether the flow rate is the cause of the cycling.

Will be back once I have some news. Thanks to you both

RE: Flow temperature up and down like a yo-yo

greekgoddj — Sun, 26 Nov 2023 11:45:53 +0000

@derek-m Outside temperature was 0 :) thermostats inside were already 1-2 degrees higher than normal to rule out the system not calling for heat in the first place. That is all of downstairs UFH and all radiators upstairs.

The filter itself didn’t look dirty, but the technician drained some fluid, stuck it in a tube that checks how clean/dirty it is and it suggesting the system may need a clean as well (odd as the entire system/house is 3.5 years old). However the technician still believes we need to change the pump first (it doesn’t “sound right” to him). So I continue to wait for Mitsubishi to send him the pump. Will update this thread then with the new rate and whether it helps the issue.

RE: Flow temperature up and down like a yo-yo

SUNandAIR — Sun, 26 Nov 2023 10:37:17 +0000

Does anybody have any thoughts? Thanks

Hi Greekgod

I thought you might have known…. All heat pumps are made by the Greek goddess of Mischief, Delusion and Folly. Have you or your installer upset her? Goddess Ate’ is her name.

As Derek is suggesting there are quite a few possible causes. But the first thing is to ensure your flow rate can reach the upper part of the range quoted by “Mischiefbishi”. Once you can achieve that range you may then be able to identify other causes.

Im a bit surprised you’re not getting a flow rate error message tbh.