Ideal boiler cycling with Nest & Opentherm

[flyingsailor]

Hi all, I have an Ideal Logic max 35 and have just connected my Nest thermostat via opentherm. The boiler modulates the water temp fine but as the heat reaches the the target temp on the thermostat, the boiler turns the flame off, keeps the pump running and then every 90-120seconds refires the flame for about 20 seconds before repeating this process for sometimes a few hours. During this time, the water temp is around 45 deg and drops down to 24/25 deg before relighting. Of note, it never did this when it was connected via on/off. Wondered if this is normal or if it’s actually bad for the boiler to constantly cycle so often. Many thanks.

 

[Knappers]

Do you have thermostatic rad valves throughout?
I guess either flow throught boiler is restricted by trvs or your heat demand is much lower than the boiler can modulate to so it cycles.
Shouldn't be a problem for the boiler tho.

 

[flyingsailor]

Hi Knappers, thanks for the reply! All rads have TRVs and are fully open. Is the boiler essentially ‘short cycling’ by doing this? I just don’t want it to reduce the lifespan of the boiler by constantly switching the burner on and off?

 

[Knappers]

It's not going to break it but will add a bit of wear so not ideal. I'm not sure on the settings for the nest, if there's any advanced settings to change heat curve or anything but If there is then maybe have a look at that?

 

[Littlejack101]

I have the exact same thing with the exact same setup - though some of my TRV's were shut some of the time which may have been my issue - testing now.

 

[flyingsailor]

I have the exact same thing with the exact same setup - though some of my TRV's were shut some of the time which may have been my issue - testing now.

Be interested to see how you get on mate! Mines still doing it so I wonder if the boiler is indeed trying to modulate at too low a temp for my system or whether the nest is doing it to just keep a bit of residual heat pumping through to maintain the requested room temp.

 

[flyingsailor]

It's not going to break it but will add a bit of wear so not ideal. I'm not sure on the settings for the nest, if there's any advanced settings to change heat curve or anything but If there is then maybe have a look at that?

Unfortunately I don’t think you can change the heat settings through nest which is frustrating

 

[Littlejack101]

Be interested to see how you get on mate! Mines still doing it so I wonder if the boiler is indeed trying to modulate at too low a temp for my system or whether the nest is doing it to just keep a bit of residual heat pumping through to maintain the requested room temp.

Still doing the same with all TRV's open...no idea whether this is working 'as designed' or an issue now!

 

[flyingsailor]

Still doing the same with all TRV's open...no idea whether this is working 'as designed' or an issue now!

How long have you had it running with this setup mate? I’ve had mine setup for about a week and a half and the last day or two, it’s done it a bit but not as much. It seems nest maybe ‘learning’ what water temp is required in order to maintain the temp of the thermostat. Rather than cycling as often it’s now holding around 48 deg flow temp as it approaches the target and then shuts off. I’ll keep an eye on it and let you know if it continues.

 

[king of pipes]

Firstly how many rads do you have ? The Ideal logic 35 kw max has a modulation rate from 8 - 24 kw in its heating mode , there must be a heat load loss through the boiler at all times we dont know how it's installed so let's say you need at least one decent size radiator with no trv fitted is this the case ?

 

[Littlejack101]

How long have you had it running with this setup mate? I’ve had mine setup for about a week and a half and the last day or two, it’s done it a bit but not as much. It seems nest maybe ‘learning’ what water temp is required in order to maintain the temp of the thermostat. Rather than cycling as often it’s now holding around 48 deg flow temp as it approaches the target and then shuts off. I’ll keep an eye on it and let you know if it continues.

I've had this setup for a week. No idea if the boiler behaved like this before as I was not really looking! I've messed around with the boilers 'Max flow temp' but that doesn't seem to make a difference.

 

[Littlejack101]

Firstly how many rads do you have ? The Ideal logic 35 kw max has a modulation rate from 8 - 24 kw in its heating mode , there must be a heat load loss through the boiler at all times we dont know how it's installed so let's say you need at least one decent size radiator with no trv fitted is this the case ?

I've got 10 rads & a couple heated towel rails. TRV's on all the rads but are fully open downstairs where the thermostat is located. The majority of the radiators are pretty old so would not surprise me if they not kicking out a huge amount of heat.

 

[king of pipes]

Opentherm should help stop the boiler cycling so much I am using it on my own system via a Nest thermostat , heating the system to a maximum of 60 °c over a longer period the boiler modulates to a very low output and condenses all the time , are you 100% sure you stat is operating in opentherm? it needs to be configured in the settings on the stat , you can then test it in the equipment setting. Kop

 

[Littlejack101]

Opentherm should help stop the boiler cycling so much I am using it on my own system via a Nest thermostat , heating the system to a maximum of 60 °c over a longer period the boiler modulates to a very low output and condenses all the time , are you 100% sure you stat is operating in opentherm? it needs to be configured in the settings on the stat , you can then test it in the equipment setting. Kop

I was 100%, but your post prompted me to double check...I hadn't realised that the stat settings needed to be changed & was set up in on/off mode. Will see what happens now, but wanted to thank you Kop - I'd totally missed the stat set up part.

 

[king of pipes]

Can be a pita to configure sometimes you need to uninstall the app and start a fresh you should see something like this once your set up . Regards Kop

 

[king of pipes]

Can be a pain to configure sometimes often it's better to uninstall the app and download it again , once your connected you should be able to see these

 

[flyingsailor]

Firstly how many rads do you have ? The Ideal logic 35 kw max has a modulation rate from 8 - 24 kw in its heating mode , there must be a heat load loss through the boiler at all times we dont know how it's installed so let's say you need at least one decent size radiator with no trv fitted is this the case ?

Thanks King, I have 12 rads in the house, a couple are fairly large column ones and all TRVs are in the fully open position. I’ve balanced the system as best I can with an average differential between flow and return to the boiler between 13-15deg.

 

[king of pipes]

Once your set up it should be fine I'd say 👍

 

[flyingsailor]

Opentherm should help stop the boiler cycling so much I am using it on my own system via a Nest thermostat , heating the system to a maximum of 60 °c over a longer period the boiler modulates to a very low output and condenses all the time , are you 100% sure you stat is operating in opentherm? it needs to be configured in the settings on the stat , you can then test it in the equipment setting. Kop

Hi kop, mine is setup exactly like this and does run for longer periods at lower temps but as the room temp reaches the target, the boiler doesn’t shut off, instead the pump runs and the flame ignites for a bit then goes out and repeats this continually. This maintains the target temp but wondered if it was normal or whether it should shut the boiler off and then restart it as the target temp drops a bit?

 

[king of pipes]

I don't think it should cycle so frequently even when it reaches its temperature set point mine doesn't Opentherm should modulate your boiler down to its lowest setting possible , review your settings on your Nest as my previous post , what boiler do you have ? it maybe possible to set a period of time your boiler heat between switchings ? Regards Kop

 

[flyingsailor]

I don't think it should cycle so frequently even when it reaches its temperature set point mine doesn't Opentherm should modulate your boiler down to its lowest setting possible , review your settings on your Nest as my previous post , what boiler do you have ? it maybe possible to set a period of time your boiler heat between switchings ? Regards Kop

All settings are the same as yours - opentherm, combi, 60 deg etc. I have an Ideal Logic Max 35. It just seems odd to me that it won’t hold just hold mid 40 deg flow temp (it can do this as I’ve checked the sensors on the boiler) until it reaches target then shut off. It stops the flame as it’s very near to target temp and keeps the pump on with the occasional kick of flame to increase the flow temp for about 20 secs.

 

[flyingsailor]

I don't think it should cycle so frequently even when it reaches its temperature set point mine doesn't Opentherm should modulate your boiler down to its lowest setting possible , review your settings on your Nest as my previous post , what boiler do you have ? it maybe possible to set a period of time your boiler heat between switchings ? Regards Kop

Hi kop, update - when the heating kicks in it will modulate low (around 37-40 deg flow) but if there is a demand for DHW when it’s running that low, it never returns to that temp and that starts the cycling. It’s as if the flame for CH starts up and gets too hot too quick (hits around 41 ish and then cuts out)

 

[speedyuk]

Hi, I'm joining in on this thread as I've just had an Ideal Logic Max Heat 2 15 boiler fitted. On day one it was commissioned in S Plan using the NEST Gen 3 that had been fitted to the previous boiler. Day 2 it was switched over to PDHW / Opentherm. It operates correctly in the two different call for heat modes but I'm getting the dreaded short cycling when the room stat approaches target temperature - grr. I went down this route after having a perfect working BAXI 600 Combi and Tado setup in my previous home. That setup was fantastic, didn't miss a beat and modulated the boiler perfectly. The 11 year old 4 bed detached property I'm in now already had unvented cylinder and 10mm microbore. It has a Grundfos UPS 15/60 pump. Pump was on III with previous boiler and left like that with new. The boiler reports a flow rate of 11l/m on III and drops to 9l/m on I. If anyone has any suggestions / new info on a cure I'd love to hear it. Thanks

 

[ShaunCorbs]

Trying running on speed 2 eg II

 

[speedyuk]

Trying running on speed 2 eg II

Hi, I've run it on 2 and now I'm down to 1 as the boiler actually reports a better flow / return differential on 1. The boiler is still short cycling. I suspect a) it can't modulate low enough for the demand and b) even if it can in certain cases it still fires too high and doesn't modulate down quick enough to catch the required output .