Ecotec Plus 831 & Honeywell CM721/BDR91

[steviebobs]

Hi again all, a little teaser you may be able to help me with?

First of all, this does not cause me a great deal of pain, more a sense of bewilderment !!

I had a new boiler (as above) fitted in September, linked to an existing Honeywell CM721 Wireless Programmable Room Thermostat and relay box.

The first time the heating was used in anger following installation was probably late October, and all appeared to work fine.

I have the programmer set at 19 degrees during the early part of the day, stepping up to 21 degrees at 3pm.

As the weather got a bit colder I noticed that at 3pm the boiler would start to do its job raising room temperature (lounge) toward the required 21 degrees but stop at 20.5 degrees. It can then take best part of 3 hours to finally get to 21. Sometimes, even after reaching 21, it can drop back to 20.5. I don't recall my old boiler (Biasi 428S) having this problem, I am sure it used to go up to 21 quickly and stay there.

I know the CM721 has a bit of clever trickery with getting near to required temperature and then cycling, but shouldn't it still get to the required 21?

Any responses are really welcome. Thanks.

SjH

 

[TCCHeating]

Its to do with TPI. You need to adjust the proportional bandwidth in the settings. Also you could increase the minimum boiler on time setting. And you could have a fiddle with the cycling settings as well. See the link below for info.

http://www.honeywelluk.com/Documents/Installation-Guide/pdf/1066.pdf

 

[steviebobs]

Thanks for that TCC

I have been reading a fair bit about TPI on this forum from posts going back to 2010, and some very interesting technical reading too!!

My Honeywell is set at the default values, so am able to have a stab at the variables mentioned, but it was case of intrigue rather than pain that made me start the thread, and the fact that I seem to be educating my installer, who wasn't particularly 'au fait' with the technicalities of the Honeywell.

I did read some advice a while ago ' fit it and forget it' !!

Thanks Again

SjH

 

[D_Hailsham]

You say that the CM721 worked OK with your previous Biasi boiler, but does not work with the new Vaillant. So it's a case of adjusting the boiler and/or the CM721 to make them work together.

TCC has suggested changes to the CM721. However I would not agree with changing the cycle time.

Do you have Optimization turned on? If you haven't, turn it on and then adjust your times so they are set to when you want the house to be up to temperature. So the AM on time would be set to 7am (when you get up) and the PM time to 5pm (when you get home from work). The CM721 calculates when the boiler should come on, taking into account how much the temperature has dropped and how long it took on previous occasions. It takes about a week to learn what to do.

It might also be worth setting the max output of the boiler to what is actually required for your house. The Vaillant has a max of 24kW, which will only be necessary if you have a large poorly insulated house.

Use the Whole House Boiler Calculator to find out the heat required in your house. Then set parameter d.000 to the correct kW value (default is "auto").

 

[steviebobs]

Thanks Mr. Hailsham.

I am going to take a little time to absorb the content of your post thoroughly and act accordingly. This morning I read a fascinating old post of about 2010 (of which you were a valuable contributor!) and have to admit to being a bit of an 'anorak' when it comes to techy issues.

I did have a few issues with my previous (loyal) boiler (the Biasi 28) and always got fantastic support from you guys (Tony Agile & co), so thanks for taking the trouble to respond.

I will come back in a few days when I have absorbed your comments.

AND, I do need to add, no fighting between you experts, this forum is renowned for it, and although as an innocent by-stander I consider it 'good sport', I don't want you guys to fall out with each other !!!

Regards to all

SjH

 

[TCCHeating]

There will be no fighting here

D_Hailsham made a good point. If it worked ok with the Biasi then the boiler settings are prob to blame rather than the room stat. Oh and yes having thought about it with a clear head, dont mess about with the cycling settings!

Posting after a night at the boozer can be hit and miss for me but there was sweet f all on the telly