Leaking MVHR + poor heat recovery - Vent Axia Sentinel Kinetic Advance S (405215)

[Novice Becky]

Vent Axia Sentinel Kinetic Advance S (405215) - The installation engineer has come back quite a few times and Vent Axia came on Monday but it's still not clear why I have this problem. Wondered whether anyone has any suggestions?

 

In colder or wetter weather (maybe both?) I have water leaking out of my MVHR unit - I've had it leaking out of drain and front of unit. Also the heat recovery seems very poor to me (eg 0 degrees outside, supply temp 11 degrees, room temp 20.5 degrees). And the machine reads a significantly higher RH than my hygrometer in a bathroom and the house doesn't feel damp (eg. 76% vs. 66% RH).

 

First of all it seemed to be working brilliantly and condensation disappeared overnight (weather was warm for December), supply air was around 19 degrees on the app.

We had a very cold spell in January and I don't think it's been working right since then. We also had ASHP installed at the start of the cold spell.

 

Last Friday it was leaking out of the front of the machine near the bottom. I took the cover off and removed the heat exchanger which had condensation on the outside and lots of water slooshing around inside it. I tipped it up and emptied most of the water out. There was also water in the RH (unused) drain which there shouldn't be as the unit is left-handed. I removed the RH blanking cap and got rid of the water. I poured a jug of water and Milton down the LH drain - def not blocked.

 

This week I removed the drain cap on the RH side and put a bowl underneath because the unit still sounded very wet after Vent Axia visit but since I drained the water that was sitting in the RH drain there's hardly been any water from the RH side (over 2 days). The weather has been warmer and dryer. I put the RH drain cap back on today. I have the installer coming to fit a drain on the RH (supposedly redundant) drain. VA engineer thought this might be a good idea even though it shouldn't be needed. The unit can be left- or right-handed depending on where you vent to the atmosphere and you use either a left or right drain.

 

Background:

• I bought an MVHR system from BPC and had it installed by someone BPC suggested in December 2023.
• retrofitting a 1961 bungalow, 134 m2
• main purpose - to get rid of condensation problem and allow me to get more airtight
• secondary purpose - heat recovery (save energy)
• unit and ducting in cold loft, ducting is insulated (25mm foil backed glass fibre - should I have got 50mm? I was told no one uses that)
• unit is mounted on the north gable wall (brick)
• this is a branched system with 125mm METAL ducting (my choice)
• 4 extracts, 7 supply vents
• commissioned normal extract 35% / supply 55% speed setting
• boost - extract 45% / 56% supply speed setting
• condensate drains into a gutter (under the eaves) because there isn't a bathroom near enough to get a 5 degree fall
• I changed filters a few weeks ago as they were very dirty.

[Novice Becky]

FROZEN CONDENSATE

The installer initially refused to insulate the condensate pipe (I told them building regs and instruction manual said this was essential) then it froze (and machine was leaking) and so they decided they would insulate the pipe (they claimed they'd never seen a loft freeze before). They didn't insulate along the entire length into the eaves so when we had the very cold weather it froze and the machine was leaking out of the RH drain cap. I was concerned that the machine had been damaged by this but Vent Axia seemed to think the machine was fine when they inspected this week. They agreed that there shouldn't be water in the RH drain. They said there was excess water coming from the duct/ducts connected to the atmosphere but they didn't know why. Their tech team said they might replace PCB but engineer didn't think that was the problem. I've never had an error message.  I've insulated the condensate pipe.

[Novice Becky]

MACHINE ON BOOST

The machine seems to be on boost the whole time (but often at a lower fan speed % than on the preset value for boost). The installer upped the fan speed on the settings to about 60% but that didn't do anything. I let it do what it wanted for several days and it continued to be on boost. The house is not damp.

This morning 7am info said 9 degrees outside, supply air temp 16 degrees. Living area was 21 degrees. RH 72% on MVHR (63% on hygrometer in bathroom)

This afternoon was unusually warm and sunny - MVHR said 17 degrees OUTSIDE (correct), supply air temp 21 degrees. Living area was 22 degrees. RH on MVHR 64% (about the same in bathroom) but machine was still on boost (intake 54%, extract 47%).

[Novice Becky]

POORLY INSULATED DUCTING TO ATMOSPHERE

Today I have closely inspected the insulation on the ducts to/from atmosphere. There are sections of uninsulated ducting on the supply and extract to atmosphere (photos). There are some areas where I don't think you can get insulation on the ducting because the ducting is right up against the brick. And some areas are covered with aluminium tape but there is no insulation under the tape. I've asked the installer to reposition the duct work so there's room for insulation. The installer is currently saying no - he says the main reason for insulating the ductwork on the air intake and exhaust to atmosphere is to stop condensation forming on the outside of the duct, not inside. Could this poorly insulated ducting be the cause?

[JohnMo]

I wouldn't put the condensate out the roof it really needs to be down a drain, it also needs a drin trap. Otherwise it will suck outside air in also, adding to the issues.

 

I can spiral wound duct without insulation, not good.

 

14 minutes ago, Novice Becky said:

supply temp 11 degrees, room temp 20.5 degrees)

If the supply and extract flows are poorly balanced the flow temperature gets messed up, these figures should be within a degree.

[dpmiller]

is the unit switching to humidity-controlled boost? try upping the humidity threshold a few %, the sensor's are n't that accurate in my experience

[Novice Becky]

14 hours ago, JohnMo said:

it also needs a drin trap

Thanks @JohnMo. Do you mean dry trap? There wasn't clearance under the machine for a dry trap. I'm lucky I have a trap at all - they are still saying it doesn't really need a trap because it's going straight outside?!

Helpful comments - I've been thinking about running the condensate to a bathroom. I've calculated I could get a fall of at least 3.3 degrees to a bathroom. Instructions say min 3 degree fall. Building regs say 5 degrees. Has anyone been ok with a 3 degree fall or do I need a pump or maybe I need to conceal the pipe at ceiling level.

[Novice Becky]

15 hours ago, JohnMo said:

I can spiral wound duct without insulation, not good

Thanks. Do you mean the large steel attenuators? I assumed they weren't insulated because they have insulation inside them. Do the attenuators need insulating?

[BotusBuild]

Becky, In a cold space like that it is best to insulate everything you can to reduce the possibility of condensation on the outside of the pipes/ducts.

 

The condensate drain pipe MUST be insulated. Well done for ignoring the installer.

 

Do try to get the condensate drain pipe to an internal drain, and not to the external guttering.

 

I fear that what happened is during the freezing conditions, the condensate pipe froze from the outside as in your picture and blocked that pipe completely. The condensate that was being collected inside the unit now had nowhere to go and so "overflowed" inside the unit to place/s where it could go, and then came out in all the wrong places. There is one good piece of news in all that - freezing conditions do not seem to be affecting the inside of your MVHR unit 🙂

 

I think that re-routing that condensate drain pipe will solve your problems

[Novice Becky]

5 hours ago, dpmiller said:

is the unit switching to humidity-controlled boost?

Thanks @dpmiller. Yes. Yesterday (warm day) it was in humidity-controlled boost all day - even when machine said RH was 61%. Humidity threshold is set to 70%. I read that the machine can go into boost even if it's below the set threshold (70%) if it detects sudden or sharp increases in humidity. But there wasn't a lot going on in the afternoon - just me at home. Surely it should have switched off boost at 61% rather than just slowed down a bit?

14 March
	Air Temp (C)
Time	external	internal	RH %	supply speed %	extract speed %	Mode
13:19	16	20	65			Humidity controlled boost
13:38	17	21	64	54	47	Humidity controlled boost
14:04	17	21	63	54	47	Humidity controlled boost
14:13	17	21	64	55	48	Humidity controlled boost
14:40	16	21	61	51	42	Humidity controlled boost
16:09	14	21	70	61	60	Humidity controlled boost
23:29	12	18	71	20	20	switched to low 8 hrs overnight
			(88% outdoor)
		(Zone 1: 22)	(Zone 1: 51%)

In the evening I discovered some extra pages on the app. See 11:30pm. Internal air temp 18C. How does it even know the room temp is 22C? There's no thermometer or hygrometer/humidistat linked to the machine but it's correct and has been correct each time I look. 18C is quite a lot colder than 22C. Room humidity is 51%? And why is machine humidity much higher 71%?  SCRAP THAT - just looked on the app. It says Zone 1 is 25C! It's actually 21C. The sun is shining. Maybe heating up the loft?

[Novice Becky]

Thanks @BotusBuild. OK I will def get the condensate to an internal drain (really irritating that the expert installer ignored me in the first place and then I doubt myself).
Your fears are the same as mine! I sent photos to installer to prove it was seriously frozen but obviously they weren't taking any blame for this. VA seemed to think it was all ok and couldn't see any installation errors other than tipping the machine back slightly (installer looked relieved at that news). I'm now not so sure. The date was being weird for a week a while ago and it wouldn't let me or the installer set the date to the correct date. It has since corrected itself. Today when I pressed the momentary boost switch with the installer here it went to 18 hours 11mins! It should be 15 mins. Does that sound like dodgy/damaged pcb?

[BotusBuild]

1 hour ago, Novice Becky said:

Today when I pressed the momentary boost switch with the installer here it went to 18 hours 11mins! It should be 15 mins. Does that sound like dodgy/damaged pcb?

I would be asking for a replacement PCB at the minimum. Something sounds wrong with the electronic brain.

[Andehh]

I got a replacement PCB from vent axia, after some random uncontrolled boosts. Their tech help were pretty user friendly.

 

It's plug and play and only took 15mins to replace, just label/photo the before you disconnect and not all the plugs are pokey yoke. Label/colour coordinate to be safe!

[JamesP]

Can you identify what the arrow is pointing to, looks like a vent and what temperature is the attic during a cold spell?

[Novice Becky]

@JamesP Thanks for looking at this. Your arrow is pointing to a VCD single blade damper (https://www.bpcventilation.com/vcd-in-line-spiral-duct-single-blade-damper) to help with balancing the air flows. 

There are 7 of them. MVHR layout attached

 

Novice Becky MVHR nov.pdf

[Novice Becky]

1 hour ago, JamesP said:

what temperature is the attic during a cold spell?

I don't have a thermometer up there but it's cold (30cm of insulation). When there was extreme cold like -7C there was ice under the machine where it had dripped. I had the boiler and hot and cold water tanks in the loft until recently but all the pipes were all lagged and seemed ok. I'll go and grab a max/min thermometer and put it up there - but we don't have any cold spells forecast at the moment.

[JamesP]

Thanks @Novice Becky for the layout. I installed a Vent Axia with manifolds suppling each room individually, hence not seen a VCD.

Going to ask a stupid question but is the VCD on the extract or supply in the loft area? 

I can only add as above the internal insulated condensate drain. 

[Novice Becky]

Thanks @JamesP. No stupid questions on this site! There's 5 VCDs on supply and 3 on extract. If you zoom in on the plan you can see them (VCD is in tiny font). You can use them to balance the system instead of twiddling the room valves. More control apparently. They simply increase/decrease the air flow. The installer added them in to the design by BPC. I didn't want to use the more popular plastic ducting because some plastics give me headaches which meant I needed a metal branched system.

Glad that people here agree with me on the condensate drain. Will get that sorted - and try to get the machine fixed.

[JamesP]

45 minutes ago, Novice Becky said:

Thanks @JamesP. No stupid questions on this site! There's 5 VCDs on supply and 3 on extract. If you zoom in on the plan you can see them (VCD is in tiny font). You can use them to balance the system instead of twiddling the room valves. More control apparently. They simply increase/decrease the air flow. The installer added them in to the design by BPC. I didn't want to use the more popular plastic ducting because some plastics give me headaches which meant I needed a metal branched system.

Glad that people here agree with me on the condensate drain. Will get that sorted - and try to get the machine fixed.

So all the VCD 's are in the loft which enables you to turn the blade manually, no air can get in. Would insulate these as well as both ducting silencers. 

[Novice Becky]

Thanks @JamesP. That's a useful suggestion. I'm pretty sure they've insulated the VCDs except for the switch/dial bit.

 

If I'd done the insulation myself I would have used 50mm. The installer said no one used 50mm because it's too hard to handle. Has anyone used 50mm instead of 25mm? I was thinking about re-insulating the whole lot to increase the insulation and ensure it's all done properly. I think I had a bad batch of aluminium tape and it's come undone in places and I expect more will come unstuck over time. Do I have to remove the existing insulation rather than go over the top of it? It's foil-backed.

[JamesP]

Hi @Novice Becky Not an expert but I think the condensation must be very high in the cold loft during winter months. I would insulate the silencers first and any obvious areas before you re-insulate the entire system. But the unit itself  is very exposed to the cold. 

[Novice Becky]

16 minutes ago, JamesP said:

But the unit itself  is very exposed to the cold.

Yes it's very exposed to the cold but this machine is supposed to be ok in a cold loft. Vent-Axia said that it doesn't need to be insulated (I could if I wanted but I didn't have to). The machine has polystyrene insulation inside. The manual says -20C to +40C. That's why I didn't build an insulated cupboard for it. The summer could be a problem though.

I thought about retrofitting an insulated cupboard for it but I'd have to get it off the wall to insulate behind the machine and then I'd have to alter the metal ducting which seems a bit of a headache!