Nuaire MVHR System Leaky Ceiling Vent

[tomaus]

Hi all,

 

I live in a 9 year old hour which has a Nuaire MRXBOX MVHR unit, the past few years I have had a reoccurring leak through the ceiling vent in one of the bedrooms. The issue only occurs in the winter in cold temperatures when the outside air temperature drops to close to freezing. Based on my reading I guess this is most likely a result of poor insulation on the ventilation pipe drop for this room, but I'm not sure what I should be looking for to find the fault and how to repair it.

 

Does anybody have any experience troubleshooting an issue like this, or a guide on how to correctly insulate the pipework?

 

Thanks in advance, Tom

[Radian]

7 minutes ago, tomaus said:

most likely a result of poor insulation on the ventilation pipe drop

You would appear to have some serious  condensation forming on the pipe. Is the heat exchanger set to summer mode? If it was set to winter and exchanging heat from the outgoing to incoming air isn't enough to keep the pipe above dew point then it's most likely due to poor insulation on that drop. But it's also testimony to the amount of water vapour in your loft. Why would that be?

[ProDave]

This will be condensation in or on that duct.

 

I am a little surprised to see it on an inlet pipe, that pipe at that point should contain "warm" air that has been heated by the heat recovered from the exhausted air.

 

I do notice that vent terminal is shut down probably too much, so the airflow will be low.

 

First you need to establish if the condensation is on the inside or outside of the pipe.

[tomaus]

2 hours ago, Radian said:

You would appear to have some serious  condensation forming on the pipe. Is the heat exchanger set to summer mode? If it was set to winter and exchanging heat from the outgoing to incoming air isn't enough to keep the pipe above dew point then it's most likely due to poor insulation on that drop. But it's also testimony to the amount of water vapour in your loft. Why would that be?

 

I wasn't aware the heat exchanger has different modes, there were no instructions left by the developers about needing to change settings on the unit.

 

2 hours ago, ProDave said:

This will be condensation in or on that duct.

 

I am a little surprised to see it on an inlet pipe, that pipe at that point should contain "warm" air that has been heated by the heat recovered from the exhausted air.

 

I do notice that vent terminal is shut down probably too much, so the airflow will be low.

 

First you need to establish if the condensation is on the inside or outside of the pipe.

Thanks, I'm fairly certain the water is on the outside of the pipe as it seems to be pooling in the loft and the water coming through the ceiling is dripping from the outside edge of the metal ring on the ceiling.

 

Interestingly this drop is no the closest to the heat exchanger and there are no signs of the damp on the other pipe drops.

[ProDave]

Post the model number of the MVHR unit and a picture of any controls you have associated with it.

 

The place you usually get condensation is the external cold air pipe going from outside to the MVHR unit.

[tomaus]

It's a Nuaire MRXBOX95-WALL, not much in the way of controls just some dials for fan speed.

 

[Radian]

 

2 hours ago, tomaus said:

It's a Nuaire MRXBOX95-WALL, not much in the way of controls just some dials for fan speed.

 

From the installation guide:

 

 

MRXBOX95B-WALL Mechanical Ventilation Unit with Heat Recovery & Summer Bypass

 

The bypass damper opens when a 230V signal is applied to the unit (via a manual switch, supplied). This opens the damper via an actuator. When the switch signal is de-activated the unit returns to its original state (air through the heat exchanger).

 

The summer bypass is designed to prevent heat recovery and feed in outside air without warming it. Not what you'd want in winter!

[tomaus]

That’s interesting, I wasn’t aware of that. The unit doesn’t have any controls for the bypass, and user manual does not mention needing to change anything in winter. 
 

Seems strange that the issue is only effecting one of the vents if it’s the bypass causing the issue.

[MJNewton]

Now that we’ve got cooler outside temperatures, what are the temperatures of the supplied air like? It should be obvious if the summer bypass is activated.

[tomaus]

I don’t have a thermometer to test with, but the air coming from the vent is colder than the ambient internal temperature. 

[Radian]

There could be a switch somewhere. If it was a DIY installation it might not be obvious or labelled. You might have to follow the cable to find out. It's a single 5-core cable and the grey wire is the one that would be connected to 230VAC via a switch. Presumably this single cable from the unit terminates in a junction box nearby.

 

As for why only one vent is leaking, it could be for several reasons. It could be that the insulation is innefective, or that an air leak in the vicinity is allowing water vapour to accumulate in the loft. It could be that they're all forming condensation but somehow it's going somewhere unseen.

[tomaus]

I’ve just been up in the loft and there definitely isn’t a switch anywhere. The unit was installed when the house was built so not a DIY job.

 

Based on the Nuaire instructions I think the bypass might be automatic, so maybe an issue with a sensor or the control board. 

[Conor]

Check that the condensate drain is clear and working. Could be condensation from the heat exchanger building up and finding the easiest way out.

 

When was the last time you changed the filters and checked the heat exchanger?

[Andehh]

Did you ever get to the bottom of this tomaus?