DHW heating up when Heating is on

[Helene]

Thanks everyone for your help - if I wanted to involve my electrician, and with my little knowledge, what should I tell him exactly? 

[sharpener]

On 20/09/2024 at 12:09, Helene said:

Hello. I've noticed from our melcloud graphs that every time the heating is on, the DHW heats up too. Which I confirmed by touching the flow pipe going into to the cylinder. 

 

Is it normal? I'm worried it's affecting the performance of the system and costing us more than it should.

 

We have a mitsubishi zubadan 14W and a unvented cylinder. 

 

Thanks in advance for any advice. 

 

N.B. the company who installed the system less than a year ago has folded so it's not an option to come back to them. 

 

I think your original post sums it up exactly!

 

However there are some tests you could still do to help diagnose the problem. This will save some electrician time on site as the tests are a bit time-consuming:

 

• Identify which valve is which. Check which valve moves under what circumstances. As upthread, the manual lever will go floppy when the valve is actuated. You cannot normally hear the valve opening but when the power is removed it whizzes shut with a very distinctive sound (which can be transmitted down the pipework over long distances, I can hear a valve in the loft shutting from the plant room).
• In heating mode does the weather compensation work i.e. does the pipe to the heating circuit get hotter as the weather gets colder? This is the important thing to verify as it will affect the running costs.
• In HW mode is the flow to the cylinder properly hot (hotter than in heating mode) and does the heating pipe also get hot? If so it is wasting energy.

[joth]

Your ecodan is driven by an FTC6 controller, white metal boxy thing. If you're comfortable taking the cover off that and getting some photos of the innards it should be possible to diagnose if the valves have been connected up incorrectly.

The FTC has 2 complimentary outputs for dhw / heating switch over. In S plan with two normally closed valves you should see one wired into each of those outputs 

They're labelled OUT4 and OUT13 on the PCB because why have one numbering scheme when you can have two? 

 

Edited November 29 by joth

[Helene]

On 29/11/2024 at 09:42, joth said:

Your ecodan is driven by an FTC6 controller, white metal boxy thing. If you're comfortable taking the cover off that and getting some photos of the innards it should be possible to diagnose if the valves have been connected up incorrectly.

The FTC has 2 complimentary outputs for dhw / heating switch over. In S plan with two normally closed valves you should see one wired into each of those outputs 

They're labelled OUT4 and OUT13 on the PCB because why have one numbering scheme when you can have two? 

 

Thanks for the advice, happy to give it a try. Should I turn off the pump completely before opening or there's no risk? I see 4 screws on the cover, I guess it's as simple as that? Hopefully... 

[joth]

If you're reasonably competent / careful (i.e. keep fingers off connections) it's safe enough to do still powered  up, but really no downside to shut it down first, esp if it's the first time you've poked about inside it.

 

While open it'd be worth tracing each of the cables back to unambiguously identify which pump/valve is connected where.

 

You only need to remove 2 screws, on the bottom edge of the front face.

[Dillsue]

On 01/12/2024 at 20:58, Helene said:

Thanks for the advice, happy to give it a try. Should I turn off the pump completely before opening or there's no risk? I see 4 screws on the cover, I guess it's as simple as that? Hopefully... 

If you need to ask whether to isolate before removing a cover, there's no question you should isolate before removing the cover.

[sharpener]

On 03/12/2024 at 12:51, Dillsue said:

If you need to ask whether to isolate before removing a cover, there's no question you should isolate before removing the cover.

 

If it's equipment I installed myself or I am completely familiar with what to expect under the cover and have a good reason to open it while it is live/operating I might consider the risk acceptable. In other circumstances no, too much chance of someone else's hardware mods or wiring springing out or coming apart, with unpredictable results.

 

Miscellaneous tips that have kept me alive for a few decades now include

• Keeping one hand in my pocket while probing connections above 12V DC.
• Not wearing a tie (or tucking it into my shirt) when near rotating machinery
• Asking permission before visiting the shop floor even in my own company and building works in progress even in my own house.

Yesterday's hazards may not be today's hazards.

[Dillsue]

4 hours ago, sharpener said:

 

If it's equipment I installed myself or I am completely familiar with what to expect under the cover and have a good reason to open it while it is live/operating I might consider the risk acceptable. In other circumstances no, too much chance of someone else's hardware mods or wiring springing out or coming apart, with unpredictable results.

But I wasnt referring to you.

 

I was commenting on Helene who says they've got very limited knowledge. Someone who sees 4 screws on an enclosure when someone experienced says theres only 2 so they maybe going into wrong enclosure. It's nuts to suggest someone with no/limited experience goes into a live enclosure when it can easily be isolated.

[sharpener]

Just trying to reinforce yr advice - which I thought rather neatly put. Sorry if it sounded bombastic.