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HRM inaccurate even after new battery and reversing polarity

Please help! I have a race in a few weeks and need to have an accurate HRM before that.

I have a Garmin 230, have been using it regularly since Jan 2016 with a chest strap and a clip-in HRM3-SS monitor. I haven't had to change the battery the whole time I've owned it but recently it has started to play up and so I put a new battery in. No change to the inaccurate readings though – I then found out about the reversing polarity trick and tried it ( but this doesn't seem to have fixed it.

The issue is, it displays wildly inaccurate readings, eg 155bpm when I'm standing. I have a good understanding of how my HR feels and know that this is incorrect. (I've also cross-checked with a heart rate app on my phone). And recently when I'm running at my usual easy pace it's been going up to 180bpm, and then down to 120bpm, both wildly above and below what I estimate my HR to actually be (around 136-140) based on breathing and previously when it worked.

This originally started happening in the cold weather 2 weeks ago when I was wearing a synthetic jacket and wonder if this has caused it to malfunction. I'm also concerned it may be the watch's fault if the battery isn't the issue?

What are my options? Do I just get a new watch, strap and HRM? Seems a waste as it's not that old yet.

Thank you!

  • The new chest strap worked for 1 run, but on my long run it seems to be back to nearly the same problem. It worked ok for the first 5 mins of my run, but then after running up a hill the reported HR kept rising to over 180bpm even after my breathing had recovered (I estimate my HR actually went up to 155bpm max). I fixed it by disconnecting the module and clipping it in again a couple of times and this seemed to work, before similar inaccurate readings occurred randomly during the rest of the run, sometimes going far lower again.

    Very frustrating – could it be the HR module? I don't think Garmin sells the HR module separately sadly.

  • What condition are the connectors on the module?

  • The right one looks ok and the left one has a few very small brown splotches underneath the clear plastic overlapping casing, could be rust I guess. But otherwise good condition. 

  • Just to update anyone with the same problem, in the end, replacing both HR module and strap fixed the issue.