So for a few rides now my 810 + much older – 5years? -Garmin chest strap have been reading ridiculous measurements – HR of 246 where my max is 178 for example – an no just the odd spike either, good 5-10 minute runs.

I’ve cleaned the strap extensively, is there anything else to consider or is it basically for the bin?

Have you changed the battery?

They tend to go mad when the battery is dying

Yes, battery was changed about a month ago, oddly enough about when these issues started appearing…

Tried the battery upside down for 10 min to reset trick? Mine has died and I have powercal (which has spikes occasionally but nothing mad) and a tickr for BLE connection to this iPad. Both have been much more reliable than the Garmin.

My Garmin HRM strap started playing up a couple of months ago, all sorts of weird behaviour, not working until 10 mins into the ride, recording a really low HR etc, changing the battery and putting the battery in the wrong way round made no difference.
In the end I bought a replacement and it’s been fine, the old one was at least 7 or 8 years old as it came with my Edge 705.
From what I’ve read the older hard strap Garmin HRM’s are more reliable that the soft strap one’s.

Tried the battery upside down for 10 min to reset trick?

According to Garmin 10 seconds is more than enough.

If its a soft strap HRM, you can replace the strap part with a Polar strap. That may be more reliable than the Garmin strap.
eg https://www.amazon.co.uk/Polar-Chest-Strap-Soft-keine/dp/B007XCLU66/
Just clip the Garmin transmitter pod onto that.

Its the older hard strap one. So battery upside down for a bit, I’ll try that.

Assume you have ruled out flappy shirt syndrome?
In terms of straps, Topeak used to sell a cheap replacement strap that you could clip existing module onto.
Or just get the new garmin strap – its much nicer.

The fix for me was to keep it clean (which you have done), put a small amount of Vaseline in the middle of it to break any surface conductivity amd finally to rotate it slightly so it sat roughly under my left nipple rather than centrally ok my chest. The rotation was the final thing that fixed it for me

Or just get the new garmin strap – its much nicer.

I found the newer soft strap would rub me raw on long runs, the older plastic one is much more comfortable. This was a couple of years ago, I don’t know if they’ve updated the design since then.

TBH I’ve never had mych luck with Garmin HR monitors when the battery dies
No matter how or who puts the new battery in the device never works reliably again. Gsrmin have been pretty good and so far I have had three new HR monitors off them under warranty. 🙂

You’ve probably thought of this one but I get that if it’s really windy/dry and the conduction between me and the strap goes. I get some comedy max heart rates.

I had a more persistent problem with my ANT+ on my 810 going a bit weird and giving erroneous data on HR and power. Mostly just dropping signal but sometimes the odd high read too. I fixed it with a factory reset.

My one, bought second hand only ever worked once, came as a package so not.too fussed
No idea what model it is but will try the battery trick. Strap is long gone though.

Well, the battery reversal worked for 1/2 hour then I was back to 244 BPM again. This was on the turbo using a USB with Trainerroad, & separately I had my 810 on as well – both tracked the incorrect HR uniformly so its the strap thats wrong.

Guess I need a new one.

Mine (second hand) is fine until there is a strong headwind, then it gets up to >220 bpm. The weird thing is it takes a bit of time to get back to normal. Any idea why?

That sounds like your extra effort to me.