Does the increased boiler firing/stop cycles prematurely age the boiler?

StavrosK

Hi,

Does the increased boiler firing/stop cycles prematurely age the boiler?

I believe that a boiler, and it's constituent parts, have an MTBF that cumulatively set an MTBF for the boiler in terms of number of firing cycles (affected by lots of other factors, to be sure) but nevertheless, doesn't the TADO controller increasing the number of firing cycles 5 fold equate to reducing the MTBF of the boiler by 80%?

And if the boiler is an older mode, and is more fragile, increase the chance of failure sooner rather than later?

eezytiger

My boiler has a minimum output of 9 kW and my heating needs today, since midnight, are just a little over 2 kW. Therefore my boiler only needs to be on for about 15 minutes per hour on average (today at least). So far, as we near midday, the boiler has fired 14 times. It may be 15 times by the time midday arrives.

Given the constraints forced by the boiler's excessive output I do not know how the cycling could be reduced further. I don't think Tado can be blamed for an oversized boiler.

Here you can see the firing pattern since midnight for the master bedroom, which is the only SRT linked to the zone controller. Temperature settings have been fixed throughout the time period - no scheduled temperature adjustments. 19C target for the past 24 hours and counting.

The only way to improve matters would be to have a boiler more suitably sized to the needs of the property. Even with temperatures below zero for days on end the cycling was unavoidable. At worst case (-5C) the house didn't need more than 5 kW. Stupid boiler - well, stupid choice of boiler. But when it was fitted eleven years ago I did not know what I know today. Nor did I have the insulation that I have today.

With all that said, it is worth noting that Tado used to fire the boiler for as little as under four minutes per cycle (3:40 with my boiler characteristics) but, as I've range rated my boiler to 9 kW, each firing cycle wasn't doing a lot, so I requested the minimum burn time to be raised to ten minutes. That does mean longer burns less frequently, so less cycling. If people are running Tado on out of the box defaults, with every SRT talking to the zone controller and able to demand heat, it could be a very different picture.

eezytiger

@StavrosK Yes, the ten minus minimum firing is arranged through support.

As for other tweaks, I haven't asked for any, but there is a known problem experienced by some, including me, where an SRT may be requesting heat and is firing the boiler, but the valve has not opened sufficiently to allow any flow to pass. I've dealt with this in my own way with the way I've set up temperature targets and independent rooms so that it is no longer a problem. For others I believe you can also put in a support call to ask for increased opening for such valves.

Montage

I think you’d struggle to gather any facts to sustain this suggestion.

wateroakley

In practice, most age/use related failures I’ve come across are the zone valves.

Reasons? 1. Age. 2. Brother in-law fiddling. 3. Boilers do fail and (for the boiler electronics) the mtbf of electrolytic capacitors halve for every 7 deg C temperature rise. 4. Can’t think of anything particular that I’d put down to a boiler firing cycle.

DM932187

@StavrosK yes, it will, but should not materially adversely affect boiler lifespan.

I’ve had to replace ignition electrode on my Viessmann, probably due due to firing rate, but the boiler’s been running with Tado for 10 years and been in for 13.

All modern stats use TPI these days, if relayed. If they’re modulating instead/as well (if WC fitted, for example) then they’ll likely cycle even if relay isn’t switching them on/off due to poor modulation ratio and low flow temp.

In a nutshell, yes, but shouldn’t be an issue.

StavrosK

@wateroakley @DM932187 I thought it likely. Just 3 weeks after I started using the boiler this winter, with the updated Tado App, the fan on the boiler seized up. The boiler is quite old, but has been serviced regularly. It might be coincidental, but I would rather have the boiler fail in 3 months rather than 3 weeks :-(

Is there any way of reverting back to the older way of boiler usage - call for heat, stay on until target temp is reached, then switch off, rather than call for heat, on, off, on off etc until either target temp reached or, if a manual call using a timer, time runs out?

StavrosK

Hi @eezytiger ,

Thanks for the info in your post, my boiler is most probably over sized also, but I can't change that now :-)

You say you "requested the minimum burn time to be raised to ten minutes" - how? is that via Tado Support or can it be done via the app or online somehow?

Any info on other tweaks that are available for the Tado defaults that might be useful?

StavrosK

Thanks @eezytiger that is very helpful. 🙂

Happy New Year !