Ecodan R32 Immersion

[kron77]

Hi! Recently installed an Ecodan R32 11kh. The DHW heating is causing me some concern. Depending on the outside temp, the immersion is kicking on. When it's mild outside, like today 12 degrees, it doesn't kick in at all to get it to 55 degrees C. When it was cold the other day, say around 6 degrees, it kicked the immersion on at 47 degrees to take it up to 55 degrees.

 

So couple of questions really. 

 

1. Is it normal for ASHPs to kick in the immersion at such a low temp (47 for example). I can understand, maybe, once a week needing it to go from 55 to 60 degrees when the system does its legionnaires cycle but 47 seems awful low to me. 

2.  When it kicks in the immersion the whole electrical component, like the box part, makes an almightly buzzing noise until it reaches temp. As I had to locate the electrical box outside of the cupboard, it's quite annoying and actually makes me worried there's going to be a fire soon. Is this normal does anyone know? 

 

Depending on the answer to number 1 - it would seem very odd to me that the benefits of using an ASHP to heat hot water would be outweighed by the inefficient immersion heater element coming on for the last N degrees. From what i've heard immersion heating will cost a bomb, so to have 80% of your hot water heated economically will be outweighed by the last 10-20% being heated by immersion. A £7000 piece of kit surely can do it without immersion to 55 degrees even when it's 6 degrees outside. 

 

Any advice greatly appreciated! 

 

[joth]

personally, I disconnected the immersion from the FTC6 and hooked it up to my own SSR solar PV diverter instead.

 

I had to dig around in menus and the dip switches to stop the FTC trying to power the immersion all the time as you say anyway, as the contactor in it makes an absolute din of a buzz which could be heard right across the house.

I have the FTC6 DHW set to 48ºC target, and also use the "smart grid" input on it when we have 4kW of excess solar available, or guests staying over, which causes it to boost the target up to 56ºC, which it can reach fine on its own even without the immersion.

 

Caveat: I live in mild Herts so haven't stressed test this with colder outdoor temperatures yet.

 

 

[ProDave]

I only heat our DHW to 48 degrees.  That temperature found by experiment to be the absolute hottest I can hold my hands under without being painful.  I can see no need for DHW being hotter than that.

 

The use of the immersion heater is probably because it is working hard to do the DHW heating and the worst ambient temperature for an ASHP is a few degrees above 0 when it is most likely to ice up and need defrosting.  It probably senses the icing issue and switches to the immersion instead.  Just lowering your target DHW temperature will reduce that, but you will probably be able to disable the use of the immersion in some settings if you really wanted to.

 

The buzzing box is a contactor.  they shouldn't make that much noise, you have a bad one.  It's unlikely to be dangerous, just annoying. You could complain to the supplier and get them to swap it and hope the next one is less noisy.

 

Many of us concluded that if you have mains treated water and an unvented water cylinder there is no need to a legionairs cycle so we have turned that function off.

 

Once it gets well below 0 icing ceases to be a problem as there is little moisture left in the air.

[Gordo]

1 hour ago, ProDave said:

I only heat our DHW to 48 degrees.  That temperature found by experiment to be the absolute hottest I can hold my hands under without being painful.  I can see no need for DHW being hotter than that.

 

The use of the immersion heater is probably because it is working hard to do the DHW heating and the worst ambient temperature for an ASHP is a few degrees above 0 when it is most likely to ice up and need defrosting.  It probably senses the icing issue and switches to the immersion instead.  Just lowering your target DHW temperature will reduce that, but you will probably be able to disable the use of the immersion in some settings if you really wanted to.

 

The buzzing box is a contactor.  they shouldn't make that much noise, you have a bad one.  It's unlikely to be dangerous, just annoying. You could complain to the supplier and get them to swap it and hope the next one is less noisy.

 

Many of us concluded that if you have mains treated water and an unvented water cylinder there is no need to a legionairs cycle so we have turned that function off.

 

Once it gets well below 0 icing ceases to be a problem as there is little moisture left in the air.

Agreed. But every week or so need to heat up to near 60 to kill bacteria I’d say.

[kron77]

thanks everyone for the replies, I have my installed coming today, this arms me with some great knowledge - probably look to get the contactor replaced and will look to lower the water temps to avoid it needing the immersion that often. 

[kron77]

Hi everyone I wanted to reply here with the latest in case anyone has this problem. This turned out to be a software issue with the FTC. My FTC was on version 12 I think and I got it upgraded to version 15 and the issue has since gone away, the immersion now only kicks in on the LP cycle. I hope this helps someone else, get Mitsubishi to come out and upgrade the FTC if you get this symptom!