Ecodan heating when not required.

[sliderule]

Our new Ecodan ASHP is heating when no heat is called. Set for Weather Comp, with Heatmiser UH8 wired to IN1, after power connection the FTC6 screen turns on only when heat is called (which indicates that the Heatmiser signal is ok). However, it heats from the start of the timer schedule whether or not heat is called (and even if the Heatmiser is disconnected), and only stops heating at the end of the timer schedule. It seems that some setting is overriding the Heatmiser signal. The wiring and settings all look ok, and the actual heating is working as expected, as is the DHW. I am waiting for the installer and expect a full reset is required but would appreciate any suggestions.

[JohnMo]

How is the ashp plumbed into the heating system, do you have a buffer for example?

 

Does your heatmiser control zone valves and/or a call for heat?

[Bozza]

Is it something to do with the heat pump being set on a timer to come on and off, in addition to the central heating system & DHW being set on a timer.  This was how my Ecodan was initially set up but my engineer persuaded me to set the pump to constant.  Effectively though the pump only comes on when the DHW or heating timer kicks in and is calling for it.  Also I think ours come on when’s it very cold as a safer measure.  I’m still a bit of a biff though when it comes to my system but wondered if this may be a factor.

[sliderule]

Thanks JohnMo, the new Ecodan which replaced a 13 year old Ecodan, is plumbed to UFH and DHW each via 2-way valves. There is no buffer tank. The Heatmiser signal wires are connected to IN1 in the FTC. They only call for heat.

Thanks Bozza, the timers are now only in the FTC, and are working ok, except that when the timer turns on the UFH, it heats immediately and continuously whether or not heat is being called, until the timer turns it off (or an upper limit is reached). The important phrase in your comment is "...and is calling for it". It seems our room thermostats/ Heatmisers are being overidden by something.

The installer is coming tomorrow, so I hope he has the answer!

[sliderule]

The installer came and spent a lot of time on the phone to mitsubishi but did not fix the problem. Then I had an idea, I bypassed the wiring with a lead direct from the FTC to the nearest Heatmiser, and everything worked ok, proving that there is a wiring issue. Should have thought of it sooner but I hadn't found a fault with my tester - it must be a high resistance short. Now waiting for the electrician to come.

 

[Conor]

Bet you there is a jumper somewhere it shouldn't be. Have a look at the circuit diagram and see what jumper / dip switch options there are. I have a totally different heat pump but that's how I forced on the heating at the start, by a bit of copper wire between two contacts. 

[sliderule]

We have identified the problem. By bypassing the house wiring with a long cable, everything works ok, showing there is a short somewhere in the house wiring. This is not easy to find, and probably requires new wiring round the outside of the house. An easier solution is to use Advanced Auto Adaptation, which does not have a connection from house thermostats. So I have been trying it out with a long cable to the little FTC box moved to the living room. It is great! Low power and no cycling on our all-UFH system. So I will order a Mitsubishi wireless controller and receiver (£167) and go for that.

[connick159]

On 22/11/2023 at 12:19, sliderule said:

We have identified the problem. By bypassing the house wiring with a long cable, everything works ok, showing there is a short somewhere in the house wiring. This is not easy to find, and probably requires new wiring round the outside of the house. An easier solution is to use Advanced Auto Adaptation, which does not have a connection from house thermostats. So I have been trying it out with a long cable to the little FTC box moved to the living room. It is great! Low power and no cycling on our all-UFH system. So I will order a Mitsubishi wireless controller and receiver (£167) and go for that.

You wouldn't have a pic of where the uh8 cable comes into IN1 on the ecodon FTC would you. I suspect my sparky has stuffed it up as my uh8 heat enable feed is not connected at all to the IN1 block. I think I need to connect the live and live switch to the block but not 100% sure. Thanks for the post and glad your problem is solved. 

Be good to hear how the remote option worked out as I'm considering the same. I have all heatmiser stats in rooms hardwired back to 2 uh8 (one in the front of house, one in back). If what you have done works well for you it'll likely be a good option for us too.