Advice for broken MVHR unit

[Dylan Woods]

Hello all,

 

I’m looking for some advice regarding a recently broken MVHR unit in my flat, model Heatrae Sadia Advance.

 

The unit is out of warranty and Baxi, who provide product support, have suggested I employ a Heating & Ventilation engineer to diagnose the problem.  

 

Before I do, I would like to attempt to resolve the issue myself, perhaps with some help from these forums. Where I am up to:

 

·        I have recently changed the filters on the unit and given the fan unit a clean.

·        I performed a reset as per the manual.

·        I note that my unit doesn’t have an LED indicator on the top (see attached photo) so I am unsure why the malfunction has happened.

·        When I turn the unit off by mains power, and then turn it back on, the unit makes a vibrating sound for around 10 seconds and then stops.

·        Baxi have recommended I check for blockages in the ducting or that I may have any issue with the motor assembly or PCB, both may need replacing.

 

My questions / thoughts from this are:

 

1.      Does anyone have experience of this issue?

2.      New components are very expensive (upwards of £550) and I have no guarantee that these will fix the problem. It seems a big risk to purchase these blindly. See links below to components.

3.      If the ducting is dirty, would this stop the unit from working altogether? We’ve had the unit for about 5 years.

4.      I found a similar looking MVHR unit (link below) and wondered if this might be a more cost effective replacement than attempting to replace individual components.  

Any help or insights would be much appreciated.

 

Or if I have come to the wrong place, guidance on where I should post this question would also be appreciated.

 

Cheers, Dylan

 

https://www.showerdoc.com/heatrae-sadia-advance-200-plus-motor-assy-7035035

https://www.heatingspareparts.com/boiler-spares/partno/7035035/507129

https://www.ventilationland.co.uk/product/27745/itho-daalderop-hru-200-eco-unit-e-rft-high-rise-200m-h.html?utm_source=googleshoppingUK&utm_campaign=googleshopping-FeedUK&gclid=Cj0KCQjw2cWgBhDYARIsALggUhqMqR2fvlrLrRGSZYLv6JYfkKiOJ4pMz7CLU8yueYthDoUlDgeQqrYaAq9gEALw_wcB

[ProDave]

I don't know this particular unit so this is just some general thoughts.

 

Are you sure the fan(s) are free to rotate, i.e. nothing you have done while changing filters has gone back wrong so they won't spin freely?

 

On my own unit, a Kingspan / mitsubishi, I know on power up it operates the bypass mechanism which goes whir whir whir for a few seconds. If it does not detect the end stop switch operate it registers that as a fault and stops.

 

 

[Temp]

I wonder what sort of motor they have in it? Might be a capacitor issue ..

 

https://www.capacitorindustries.com/resources/motor-capacitor-types/

 

https://www.pumpspluscapecoral.com/post/how-to-tell-when-your-motor-capacitor-goes-bad#:~:text=If a run capacitor fails,it needs to operate correctly.

 

[Temp]

Looks like the same motor is used by Baxi, Main, Thorn, Potterton, Myson, Valor etc Unfortunately all seem to be charging near to the same price or more.

 

 

 

 

 

[Post and beam]

What changed?

You put filters in it

What changed ?

It stopped working

Take the filters out completely and see if it spins up. Come back when you have done this test

[jfb]

Surely you can temporarily take the ducts off so that you can rule them out as a problem

[Dylan Woods]

Hi all, 

 

Really appreciate all of your replies. Food for thought. In response: 

 

ProDave - I have removed the fan and it seems free to rotate. Changing the filters seems pretty fool proof so yes, pretty certain they're in correctly.  

 

Temp - thanks for the links, I'll try and figure out if its a capacitor issue. Do you think this is something a layman could realistically diagnose and repair? 

 

Post and beam - I took the filters out, turned the main off and then back. It did the same vibrating noise for 10 or so seconds, I then tried to activate the unit via switch and it still doesn't spin

 

jfb - I have taken the unit away from the ducting and dismantled it. Whilst doing this I attempted to turn the power on without ducting connected, unfortunately no luck. 

 

I have attached a couple of images from the manual, if of any use to anyone. 

 

Thanks all again. 

 

Dylan 

 

[dpmiller]

that's two independent fans back-to-back isn't it? And both are free to rotate? Might you have disturbed or damaged the temperature sensor?

[Dylan Woods]

Hi dpmiller,

 

Thanks for the input. Yes, it is two back to back fans and they seem free to rotate all fine. 

 

How would you work out if the temperature sensor has been damaged or disturbed? 

 

Cheers, Dylan 

[Temp]

On 16/03/2023 at 21:29, Dylan Woods said:

Temp - thanks for the links, I'll try and figure out if its a capacitor issue. Do you think this is something a layman could realistically diagnose and repair? 

 

Try other things first. Im comfortable working with a multi meter on live equipment but you might not be. It is quite dangerous after all. If there is no obvious mechanical reason why they aren't running I'd check the motor is free to rotate by spinning it by hand. Then check the motor is getting power with a meter. If it is then see how the capacitors (if any) are fitted. Some are soldered internally, some have screw terminals. If you think you can replace them they aren't usually expensive and worth doing before replacing a whole motor.

 

Other things to check with power off..

 

I dont think any MVHR motors are likely to have carbon brushes but that's something I'd also check. 

 

Our system has a fuse in the controller. Some systems have a thermal cut out. I'd hope they used one with an automatic reset but others have a button. The can be all different shapes and sizes but something with two terminals/wires and a button is likely to be a cut out. If its tripped it will be open circuit (infinite resistance between the terminals). Find the reason for overheating, fix it and push the button.

 

 

35 minutes ago, Dylan Woods said:

Hi dpmiller,

 

Thanks for the input. Yes, it is two back to back fans and they seem free to rotate all fine. 

 

How would you work out if the temperature sensor has been damaged or disturbed? 

 

Cheers, Dylan 

 

Temperature sensors are frequently a type of resistor that varies with temperature called an NTC. So look for a probe in the airflow with two wires. The resistance will probably be 10kOhms at 25c but there are many other standards like 20kOhm or even 100kOkm at 25c. Sometimes the nominal value is marked on them. Check for open and short circuit. Unfortunately I've seen them fail in a way that's not obvious. The resistance was like 9k when it should have been nearer 10k. Again they aren't expensive to replace if you can find the right one.

[ProDave]

Another for the "feeling brave"

 

When it first turns on and makes it's vibrating noise, while it is making that noise, try spinning the fans NOT with your hand, some form of push rod or stick.  If they start running that is a sure sign the start capacitor has failed.

 

(I must get around to changing the cap on my pillar drill that needs a spin.....)

[PaulHol]

Hi @Dylan Woods

 

What did you end up doing in the end? I have the same issue.

 

Any advice very much appreciated

On 18/03/2023 at 10:49, Dylan Woods said:

Hi dpmiller,

 

Thanks for the input. Yes, it is two back to back fans and they seem free to rotate all fine. 

 

How would you work out if the temperature sensor has been damaged or disturbed? 

 

Cheers, Dylan 

 

[smokinggoldfish]

I don't know if this was resolved - but this might be helpful:

 

I have the same problem, and took the motor and bypass valve out of the case to test. The clicking noise is the bypass valve going through a test routine. Once this is done it should send a signal to the motor to start. In my case the valve operates OK but the motor does not run. The fans rotate freely so either the motor has failed or the circuit board (more likely) has failed. But although the board is listed as a spare it is not available, and the only solution is to buy a new motor module complete. I am baulking at the cost (about £700!!!) and have seen elsewhere on this site that there may be some compatibility problems. It looks as though Baxi is just milking this situation. I can't believe that the manufacturing cost of the motor module is more than about £100. 

[ProDave]

25 minutes ago, smokinggoldfish said:

I don't know if this was resolved - but this might be helpful:

 

I have the same problem, and took the motor and bypass valve out of the case to test. The clicking noise is the bypass valve going through a test routine. Once this is done it should send a signal to the motor to start. In my case the valve operates OK but the motor does not run. The fans rotate freely so either the motor has failed or the circuit board (more likely) has failed. But although the board is listed as a spare it is not available, and the only solution is to buy a new motor module complete. I am baulking at the cost (about £700!!!) and have seen elsewhere on this site that there may be some compatibility problems. It looks as though Baxi is just milking this situation. I can't believe that the manufacturing cost of the motor module is more than about £100. 

Start by identifying a switch or sensor somewhere on the bypass module that should be making or breaking a contact to show the bypass module has activated.  Once you have found that identify if any voltage is being sent to the switch or sensor and then see if it is switching it's output accordingly.  It could be a faulty sensor or a faulty mechanical part so something is not reaching the expected travel to activate it.

 

If that appears to be switching properly, then you are into the realms of tracing what the circuit board is doing with that, i.e is it trying to switch a relay that might have failed.

[smokinggoldfish]

Thanks ProDave. I took the bypass valve to bits. The drive is a six wire motor, I guess a stepper. There are no switches so I guess the start-up routine is controlled by some software in the main motor module. I don't have a scope so can't see waveforms. I think my options are 1. Buy a new motor module for about £720 (!) or 2. Replace the Heat Rae Sadia unit with that of another manufacturer e.g. Domus or Nuaire for £1000 to £1500 and hope for better reliability. Any comments?

[PaulHol]

On 13/10/2023 at 13:04, smokinggoldfish said:

Thanks ProDave. I took the bypass valve to bits. The drive is a six wire motor, I guess a stepper. There are no switches so I guess the start-up routine is controlled by some software in the main motor module. I don't have a scope so can't see waveforms. I think my options are 1. Buy a new motor module for about £720 (!) or 2. Replace the Heat Rae Sadia unit with that of another manufacturer e.g. Domus or Nuaire for £1000 to £1500 and hope for better reliability. Any comments?

 

Any luck? I have the same conundrum of not wishing to pay £600 for a whole new unit  @smokinggoldfish @Dylan Woods

Edited November 2, 2023 by PaulHol

[Sgot Yaflowrates]

Hi, I just signed up to build hub today and I can already see someone who I can help!! 

I am a ventilation engineer who has now solely concentrated on installing, domestic ventilation for the last 7 yrs and had the luck to be involved in many different applications of nearly all the products that are currently on the market. 

I have had a few issues with itho advance but luckily I had a stock of replacement fan modules. 

I havn't touched them in 5yrs but I'll dig em out and give them a thorough functionality check. 

They are unused (as new), so I can help by getting a replacement to you sharpish and get your system back up and happy. 

I'm based in Anglia but am quite proficient in my explanatory skills to help you solve this issue remotely. 

Let me know if I can help. 

Scott 07586 993232

 

 

[TimEtherington]

  @Dylan Woods I share your pain. I’ve had two units fail, with the same symptoms, each after 5 years.  I stripped down the last one and found moisture damage within the fan motor, affecting a circuit board which tells the main circuit the speed the fan is running.  

@Sgot Yaflowrates - do you still have any of your replacement stock available?

[Dylan Woods]

@TimEtherington did you manage a successful repair after stripping down and finding the fault? 

[TimEtherington]

@Dylan Woods Unfortunately not.  I’ve been unable to establish the component values or find the circuit diagram.  My options seem to be the same as yours - replace the fan or the whole unit. For financial reasons I am probably going with the former.