DHW heating up when Heating is on

[Helene]

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. 

[Beelbeebub]

It sounds like your diverted valve isn't working properly. 

 

Also check if your heating is getting warm when the DHW is on. 

[Helene]

34 minutes ago, Beelbeebub said:

It sounds like your diverted valve isn't working properly. 

 

Also check if your heating is getting warm when the DHW is on. 

Thank you.

 

The heating isn't warm but we had this problem a few months ago (now solved just by changing the lever position). I only realised this new problem since we got the melcloud wifi controler installed. What do you think I should do? 

[Beelbeebub]

Bit difficult to say without a look but the problem could be that the.diverter valve isn't diverting the flow to the heating circuit so some water is flowing through the DHW circuit. 

 

Some tests to do

 

What happens when the DHW cycle is on. Does any hot water go to the heating? 

 

Does the valve move at all between modes?

 

If the vlave isn't moving it could be the vlave has a fault, either physically stuck or maybe the seal isn't working properly so some water is sneaking past. Or it could be the actuator - maybe that has a fault. 

 

If that is all working OK, it could be an issue with the signal going to the valve. 

 

You mentioned a new. Controller has been fitted. Has this been wired up correctly? Are the connections tight? Has it been configured correctly? 

 

Sorry it's not more helpful. 

 

 

[Helene]

It is helpful thanks, though I think I'll definitely need someone to have a look. For a gas boiler it's quite easy, I would just need to get a gas certified plumber out, but for a heat pump it sounds more daunting.

 

I've added two pictures, which I think are valves, do you know which one would be the one potentially related to the issue?

 

As per the controller, I think it wasn't something major, just adding the wifi device so I don't think it changed anything. 

[Beelbeebub]

It looks like you have an S plan layout. 

 

Each of those valves are basically on/off valves that either let the water flow through or don't. 

 

For the old gas systems there were 3 modes 

 

Heating only - heating valve on, DHW off

DHW only - heating valve off, DHW valve on

Split - both valves on. 

 

This worked because the flow temperature was set by the DHW demand ie. About 65C

 

For heat pump systems you only have heating or DHW on at any one time as the flow temp is differnt for heating and DHW (usually). 

 

So it's possible that a) your DHW valve is stuck open, or at at least is leaking some flow past. B) your system is acting as if it was a gas boiler and trying to do both. 

 

The thing to check is if the DHW valve is activating when in heating mode. You can do this by listening for the motor wjen it switches or by fiddling with the lever. If the lever flops about the valvle has a to activated. If it is stiff then it hasn't. 

 

. 

 

 

[IGP]

Get a heat geek to take a look, they’ll be able to sort the valve but also advise adjust the system to get the best out of it. 

[JamesPa]

1 hour ago, IGP said:

Get a heat geek to take a look, they’ll be able to sort the valve but also advise adjust the system to get the best out of it. 

That comment, while quite probably true, is scary. 

 

Do we really conclude that your local plumber can't cope with diagnosing a fault in a couple of standard valves?  This is very, very simple plumbing, not rocket science and nothing really to do with heat pumps (same principles apply to any boiler with variable flow temperature/weather compensation); plumbers use these valves all the time.  Are they really incapable of making the leap?

 

Sadly possibly we do reach that conclusion.

Edited September 21 by JamesPa

[marshian]

1 hour ago, Beelbeebub said:

It looks like you have an S plan layout. 

 

Each of those valves are basically on/off valves that either let the water flow through or don't. 

 

For the old gas systems there were 3 modes 

 

Heating only - heating valve on, DHW off

DHW only - heating valve off, DHW valve on

Split - both valves on. 

 

This worked because the flow temperature was set by the DHW demand ie. About 65C

 

For heat pump systems you only have heating or DHW on at any one time as the flow temp is differnt for heating and DHW (usually). 

 

So it's possible that a) your DHW valve is stuck open, or at at least is leaking some flow past. B) your system is acting as if it was a gas boiler and trying to do both. 

 

The thing to check is if the DHW valve is activating when in heating mode. You can do this by listening for the motor wjen it switches or by fiddling with the lever. If the lever flops about the valvle has a to activated. If it is stiff then it hasn't. 

 

. 

 

 

Might be X plan with NO for CH and NC for HW (two different valve bodies makes me think that as if two valves look identical I’d say both are NC type but with two different looking valve bodies I’d put a quid on them being functionally different)

 

NO - Normally Open

NC - Normally Closed

[marshian]

12 minutes ago, JamesPa said:

That comment, while quite probably true, is scary. 

 

Do we really conclude that your local plumber can't cope with diagnosing a fault in a couple of standard valves?  This is very, very simple plumbing, not rocket science and plumbers use these valves all the time.

 

Sadly possibly we do reach that conclusion.

It’s very sad I agree

[MrPotts]

6 hours ago, marshian said:

Might be X plan with NO for CH and NC for HW (two different valve bodies makes me think that as if two valves look identical I’d say both are NC type but with two different looking valve bodies I’d put a quid on them being functionally different)

 

NO - Normally Open

NC - Normally Closed

You just lost a quid! They are both normally closed valves.  EPH don't make a NO motorised valve, Honeywell do however the Honeywell NO motorised valve doesn't have a lever and the power cable exits the motor body at the opposite end to where the lever would have been on a Honeywell NC motorised valve.

Edited September 21 by MrPotts

[MrPotts]

8 hours ago, Beelbeebub said:

It looks like you have an S plan layout. 

 

Each of those valves are basically on/off valves that either let the water flow through or don't. 

 

For the old gas systems there were 3 modes 

 

Heating only - heating valve on, DHW off

DHW only - heating valve off, DHW valve on

Split - both valves on. 

 

This worked because the flow temperature was set by the DHW demand ie. About 65C

 

For heat pump systems you only have heating or DHW on at any one time as the flow temp is differnt for heating and DHW (usually). 

 

So it's possible that a) your DHW valve is stuck open, or at at least is leaking some flow past. B) your system is acting as if it was a gas boiler and trying to do both. 

 

The thing to check is if the DHW valve is activating when in heating mode. You can do this by listening for the motor wjen it switches or by fiddling with the lever. If the lever flops about the valvle has a to activated. If it is stiff then it hasn't. 

 

. 

 

 

If this is an Splan then it needs the pipework reconfiguring and the 2 port motorised valves replacing with a single motorised diverter valve.

[JamesPa]

1 hour ago, MrPotts said:

If this is an Splan then it needs the pipework reconfiguring and the 2 port motorised valves replacing with a single motorised diverter valve.

Or, much easier (if it has been miswired as s plan) organise for one to be off when the other is on.  At most this needs a relay and depending on the contacts available not even that.  No plumbing needed.

 

However first check nothing is malfunctioning before concluding a mis-wire

[marshian]

2 hours ago, MrPotts said:

You just lost a quid! They are both normally closed valves.  EPH don't make a NO motorised valve, Honeywell do however the Honeywell NO motorised valve doesn't have a lever and the power cable exits the motor body at the opposite end to where the lever would have been on a Honeywell NC motorised valve.

Thanks for the knowledge - appreciated

I’ll add it to the cat sanctuary charity donation I make every year instead of sending Xmas cards to people I know. Always feels like a much nicer thing to do at Xmas

 

 

[MrPotts]

2 hours ago, JamesPa said:

Or, much easier (if it has been miswired as s plan) organise for one to be off when the other is on.  At most this needs a relay and depending on the contacts available not even that.  No plumbing needed.

 

However first check nothing is malfunctioning before concluding a mis-wire

Or replace the CH MV with a NO MV and rewire correctly so that the DHW MV closes the CH MV when it is energised.

[JamesPa]

2 hours ago, MrPotts said:

Or replace the CH MV with a NO MV and rewire correctly so that the DHW MV closes the CH MV when it is energised.

Yep that also.  Either way probably easier than re orientation of the pipework to fit a diverter valve.  Which to choose depends on whether you prefer plumbing or wiring. I know which I would choose but others will doubtless choose the plumbing.

 

[marshian]

2 hours ago, MrPotts said:

Or replace the CH MV with a NO MV and rewire correctly so that the DHW MV closes the CH MV when it is energised.

 

Exactly as I spec'd my new boiler to be set up - shame the Viessmann specialist ignored what I asked for and set it up as a fecking S plan

 

Still next Friday he gets to do again - this time as I asked..........................

[Dave Jones]

pull off the 3 way solenoid, set system to dhw and not which direction the solenoid turns. manually turn the valve to DHW position and refit solenoid so when it returns to heating its turning the right way.

[Nickfromwales]

23 hours ago, MrPotts said:

If this is an Splan then it needs the pipework reconfiguring and the 2 port motorised valves replacing with a single motorised diverter valve.

Not at all. I plumb all these with 2-port and don’t really like 3-ports tbh. 
The 3-port when used is a diverter valve, not a mid-position a-la a standard 3-port in a regular heating install where overrun is required after a ‘burn’. 
 

No reason whatsoever why any competent plumber (or very good electrician) couldn’t sort this in a day (including investigative time).

 

Is this problem new or do you not know if it has done this from day 1? My guess is it is an error from the installer which you’ve not been aware of, ergo not a fault, more an mis-configuration. 

[Nickfromwales]

20 hours ago, MrPotts said:

Or replace the CH MV with a NO MV and rewire correctly so that the DHW MV closes the CH MV when it is energised.

At worst this would just require a £20 relay and base to allow the live feed to ‘flip-flop” between the 2 demands. 
 

An hour or 2 for an electrician if he knows what needs to be done. 
 

Very likely this can be done by just wiring it correctly to the OEM control board tbf. 

[Beelbeebub]

The old approach to central heating and DHW control was very mechatronic.

 

All the logic was done via cams closing switches and driving motors etc. 

 

The 3 port mid position valve was a very clever solution to the problems that posed but IMHO it can all be done these days with 2port valves directly wired to the (microprocessor) controller. The only need for the micro switches is then simply as confirmation the valve has opened/closed. 

 

A very simple system can be done with a 3 port valve just driven full A or B but if you ever need a 2nd heating zone (eg upstairs radiators) you might as well go with all 2 port valves (S plus I think it used to be called). 

[Helene]

2 hours ago, Nickfromwales said:

Not at all. I plumb all these with 2-port and don’t really like 3-ports tbh. 
The 3-port when used is a diverter valve, not a mid-position a-la a standard 3-port in a regular heating install where overrun is required after a ‘burn’. 
 

No reason whatsoever why any competent plumber (or very good electrician) couldn’t sort this in a day (including investigative time).

 

Is this problem new or do you not know if it has done this from day 1? My guess is it is an error from the installer which you’ve not been aware of, ergo not a fault, more an mis-configuration. 

I can't know for sure if it's new, as our melcloud wifi controler was only fitted in June, and this allows to see the data with some graphs, and it doesn't go back in time. As we didn't use much heating since, I couldn't notice any issue while the hot water was on but it might have been there from day 1 (a year ago) indeed. 

 

As it's not an option to get the installers back, do you suggest I get an electrician or a plumber in first? I think our plumber doesn't want to go anywhere near our heat pump as it can void mitsubishi warranty if he does something wrong...

 

We're in Leeds so if anyone has any local recommendations... 

 

Also, what is the impact on heating performance? Is it costing much more, is it reducing the flow? Trying to see if it's an actual big deal or not. 

 

Thanks!

[sharpener]

17 hours ago, Helene said:

Also, what is the impact on heating performance? Is it costing much more, is it reducing the flow? Trying to see if it's an actual big deal or not. 

 

Depends. If the heating flow is at the temp you would expect and is hotter when the outside temp gets colder then your weather compensation is working OK. At worst the flow through the DHW coil may abstract some heat from the tank but if you have enough HW for yr needs then nothing to worry about.

 

If the heating flow is at a fixed high temp, 50 or more then there is a hardware problem and/or the weather comp is not set up correctly.

 

I would try and find a heating electrician with (your type of) heat pump experience, it may just be a question of rewiring the valve or adding a relay. A plumber is more likely to want to change the valves which will be more disruptive and cost you more.

[Nickfromwales]

On 22/09/2024 at 18:57, Helene said:

I can't know for sure if it's new, as our melcloud wifi controler was only fitted in June, and this allows to see the data with some graphs, and it doesn't go back in time. As we didn't use much heating since, I couldn't notice any issue while the hot water was on but it might have been there from day 1 (a year ago) indeed. 

 

As it's not an option to get the installers back, do you suggest I get an electrician or a plumber in first? I think our plumber doesn't want to go anywhere near our heat pump as it can void mitsubishi warranty if he does something wrong...

 

We're in Leeds so if anyone has any local recommendations... 

 

Also, what is the impact on heating performance? Is it costing much more, is it reducing the flow? Trying to see if it's an actual big deal or not. 

 

Thanks!

The impact is severe for DHW, so it needs to be addressed. Apologies for the delayed reply, life continues to get in the way