Flext L4x MVHR unit

[Rekusu]

What ho one and all,

When I built our house, I installed a Flexit L4X (sometimes labelled as Helios KWLC 350) ventilation and heat recovery unit. Has been working fine for 12 years.

Recently, when it comes on, the upper Alarm LED on the control panel is illuminated; according to the instruction manual, this relates to the overheating thermostat. By turning the unit off, resetting the thermostat by pressing the reset button and turning on, all is fine. And perhaps it will be fine for the next running cycles, but it also may not and the overheating alarm will display.

There are two stats next to each other on the air inlet side which I understand to be related to frost protection; one has a reset button, the other does not. The stat with the button has continuity so I assume is working; the other has no continuity, so perhaps it needs replacing?

This evening, it started with no problems so I checked the stats continuity. Still the same as above. Disconnected one wire on the reset stat and of course, the unit stopped. Started it again and disconnected the cable on the other stat without the button and nothing happened, the unit continued to run.

So I don't know what is causing the overheating warning. Should both stats have continuity? If one does not, why is it installed?

Should I replace the non-continuity stat?

Grateful for your suggestions.

Thanks and toodle pip

 

[jj4091]

Any thermostat should have continuity at some stage if operating correctly, but if one does not then that could be the frost stat.,which would only have continuity when it drops below the designated temperature & is possibly why it has no effect when disconnected. I cannot tell you what the problem is but those resettable type stats do fail on other products ( eg. tumble drier ). Is it possible you have a restricted air flow in that area. In not my guess would be to change both stats as they are not usually an expensive item.

 

[robinbanks]

if you're interested in checking a stat you need to do so at multiple different temperatures - freeze it, try it at room temp, try it in hot water..

I suspect your stats might be like a bimetallic strip type - at room temp the frost stat has no continuity. Cool it down a lot and the strip will bend, making continuity.

To simulate the frost stat detecting a cold condition you'd short the the stat terminals together

Of the two stats I'd imagine it is the resettable one that has the issue. If literally all you have to do to get the unit working again is reset the stat, test it next time the unit is stopped because of overheat and see if its continuity is different to now

 

[Rekusu]

Thank you soooooo much for the replies. Never considered that the frost stat would be open in normal conditions but makes perfect sense.

Will test the stat next time it happens, but of course, having removed both stats, looked at them and wiped a damp rag across the base, over the past 24 hrs, the unit has been working fine! Sods Law.