Remeha boilers and Honeywell CM9XX thermostats

[D_Hailsham]

Does anyone have any real-time experience of using a Honeywell CM9XX programmable thermostat to control a Remeha boiler?

There have been suggestions that they are not compatible due to the way the Remeha controls modulation.

 

[Dan Robinson]

Can't think of a feasible reason why there would be a problem.

The controls are just providing an On/Off signal. I doubt it modulates any differently to other boilers.

 

[D_Hailsham]

The controls are just providing an On/Off signal.

But it's not like a traditional stat which keeps the boiler on until the room is up to temperature and then turns off. The CM927 will run the boiler flat out until the room temperature is 1.5 degrees below target. At this point it will cycle the boiler on a 10 minute cycle, initially 9 minutes on 1 minute off, reducing the on time and increasing the off time as the room temperature nears the target temperature.

I doubt it modulates any differently to other boilers.

It appear that Remeha boilers start off at a mid point output and then modulates up or down to the correct output according to the change in water temperature. This can take several minutes

Obviously, if the stat ON time is very short, the boiler will not have reached the correct modulation point before the stat turns the boiler off. again.

 

[Dan Robinson]

Pretty much as I thought then .

You can always change the on/off cycle times.

 

[D_Hailsham]

Pretty much as I thought then .

That wasn't the implication of your earlier reply.

You can always change the on/off cycle times.

Thought of that. I have emailed Honeywell and Remeha asking for their comments.

 

[mysteryman]

Better in that case to have the manufacturer's own weather compensation.

 

[Dan Robinson]

Well I assumed the boiler doesn't fire at full tilt. Granted - mid point is a little odd, but not as odd as a 4 series Vaillant .

As MM posted - bung a weather sensor on the boiler and it should mitigate any cycling issues.

It certainly won't be significantly different to most other boilers.

 

[D_Hailsham]

MM: "Better in that case to have the manufacturer's own weather compensation."

D_R: "bung a weather sensor on the boiler and it should mitigate any cycling issues."

Sorry, but they are examples of the "this is the solution, what's the problem?", cart before the horse, approach.

As I said in my opening post:

"There have been suggestions that they are not compatible due to the way the Remeha controls modulation.

Does anyone have any real-time experience of using a Honeywell CM9XX programmable thermostat to control a Remeha boiler?"

It is obvious that neither of you have the requisite real-time experience of such a set-up and are therefore advocating solutions before we know if a problem exists and what, exactly, it is.

 

[mysteryman]

If you want effective control on a modulating boiler, it is obviously better to use the manufacturer's equipment. Anything else is a compromise.

 

[D_Hailsham]

Reply from Honeywell

The CM927 is made for combination boilers so the technology should be compatible. Normally the boiler would have connections for external controls.

If in any doubt contact Remeha with our attached spec

Useful - I don't think!

 

[Dan Robinson]

What do you want them to say? They don't know what the boiler software is set to do.


Hell, I only fit boilers and controls for a living. What do i know?

 

[ServiceNumpty]

All my remeha installs have honeywell CMT921'S, no phonecalls from my customers saying the boilers cycling. Mind most wouldn't notice because they're in Airing cupboards, very few in Kitchens.

 

[ALEC1]

the broag starts low an ramps up ove a fixed time. When the return starts to rise, it stops ramping up... just like the atag..

I can imagine that this is what the comment refers too..


why not do the isense or honeywell OT themeostat instead? I cant see the point of using a compensation controller to control a boiler that accepts compenstion controls but with an on off signal..

 

[simond]

Here we go again - the post was not about WC, Alec. Do you have any interests outside this narrow subject?

We fit 9 series Honeywell stats on most installs (except WC ones, Alec) and haven't had any problems with them working in conjunction with Remeha units.

The Remeha weather comp set up is one of the most flexible out there; in fact the installation featured in their brochure with WC is one of ours, pictures taken on site in 2007.

Not a great fan of their boilers. They used to be promoted by lots of tradesmen (and cretins masquerading as tradesmen) on this forum some years ago. I think Remehas suffer from being cheap, in both senses of the word.

 

[ALEC1]

My point is that the cm9xx series is a variation of the OT version, just with the OT removed and changed to on-off switching...The board of the remeha is OT, the cm9xx has compensation logic the only thing thats not there is the OT connection...

Nothing to do with weather compensation... compensation controls can be indoor, out door or both!

and yes it does fascinate me the lengths manufacturers go to to keep good products from the market...presumably because the want to avoid the support costs of developing a new market...