Correct boiler setting

[jpm777]

I'm trying to get it to work well with my very sensitive Honeywell DT90e thermostat. It seems to bring the boiler on all the time, even when the house hasn't dropped temperature. When the boiler fires for 1 minute or so, the radiators don't even get warm to maintain the temperature and it seems like a waste of gas and unnecessary stress on the system constantly firing every 5 or 6 minutes.

Your Honeywell stat's not sensitive, it just uses dodgy TPI operation to turn the boiler on and off according to the amount of time that it thinks your boiler needs to maintain the set temp. THis is unlike normal stats that just monitor the actual temp and bring the boiler on and off to maintain the set temp. Typical example of something that sounds clever, but in practice is impractical.

The TPI system is flawed, difficult to explain to customers, supposed to be more energy efficient but wastes it in other ways, creates unnecessary noise and wear and tear and can be annoying if the boiler is audible from rooms in house. TPI makes the boiler fire up for no reason and can sometimes fire the boiler every 4 mins. Exactly the symptoms you describe.

I won't recommend Honeywell any more, as the TPI can't be turned off. However, other manufacturers have stats with similar operation to TPI, but importantly, this can be turned off to allow the stat to work like a normal stat.

I prefer the Drayton Mistat range, as their version of TPI (Chrono Proportional Control) can be switched off on their stats, to allow them to act like a normal stats. This prevents unnecessary boiler firing, etc, etc. I would bin your stat and fit a Drayton.

http://www.draytoncontrols.co.uk/mi-series-mi-stat-room/[/QUOTE]

Hi Whitespirit66,

Interesting you should say that about the Honeywell stat. I've tried experimenting in detail with the settings to no avail. I'm not a technophobe I promise! What frustrates me the most is that my boiler is constantly firing, yet the radiators never get hot. When I change tact and boost the heating when needed to keep a similar temperature, it costs a lot less. I was puzzled that a supposedly energy efficient system was costing me more to run. I guess that the answer is that the stat cannot provide me (whether it is due to the non-condensing boiler or not) with the best solution for my house. It seems a real shame that something that is meant to be so good doesn't appear to work in practise...

Thank you for the link to the Drayton stats. Do you think one that I can turn the TPI off is better than a more basic one? If so do you have any recommendations?

The problems that you are experiencing are exactly the same as I have found with this operating system.

If you need a wired stat, the Danfoss RET-B (not the RF version) has selectable chrono p. Or if wireless, the Drayton is good and is the latest technology but operating as a proper stat. These digital stats will provide more accurate control than the traditional dial stats.

http://www.heatingcontrolsonline.co...nfoss-randall-retb-room-thermostat-p-243.html

Hope this helps.

Very helpful thank you!

One final question please... My stat is wired. Do you think the wired danfoss would be better than the Drayton and changing to wireless ? I am aware of the difference and think it may be better wireless and having the stat in my lounge, but am unsure about the different installation cost. The wired one I would fit myself, the wireless one I would get a reputable central heating engineer in to fit.

Thank you again.

 

[jpm777]

TPI in conjunction with an SE boiler (non condensing)? , would be checking the hex for corrosion (back end rot).

Tut tut.

Hi,

Is the tpi stat with a WB 19/24cbi non condensing boiler a "no no" then?

 

[Steelmasons]

TPI with any type of non condensing boiler is a not advisable , flue gasses will condense below 50c block temp (6% CO2) , sustained low temps will corrode the hex whether it be copper or cast iron , especially copper , have you noticed any green residue building up on hex????

 

[jpm777]

TPI with any type of non condensing boiler is a not advisable , flue gasses will condense below 50c block temp (6% CO2) , sustained low temps will corrode the hex whether it be copper or cast iron , especially copper , have you noticed any green residue building up on hex????

I haven't noticed any corrosion on the heat exchanger. The WB 19/24 cbi has a cast iron heat exchanger and when I checked a year ago was fine.

 

[fullofit]

There is nothing wrong with Honeywell TPI. You need to set the stat cycle rate to once every 20 minutes (Cr=3).

 

[jpm777]

Thanks Fullofit,

I have experimented with all the settings and changed the cycle rate per hour to 3 to bring down the amount of time the boiler fires.
Unfortunately the boiler still fires (allbeit a little less often) however it still fires the boiler for only about one minute to two minutes and the radiators aren't able to heat up in that time.
The temperature in the house does not drop whether it is set like this or whether I turn the heating off altogether (for a period of at least an hour). Thus the very fact that it fires and doesn't need to is a waste of money, which is why I feel the stat is too sensitive.

 

[Dan Robinson]

Sounds to me like it's doing what it's supposed to.

It is maintaining the temperature it is set to. Detecting the start of the temperature drop and firing the boiler accordingly.

 

[jpm777]

Hi Dan,

Thanks for the reply. I would agree it is acting as supposed to if only the temperature did actually drop when I turn the heating off.
As this doesn't happen for more than an hour with the temperature outside greater than 6c, it does seem that the stat is too sensitive and wasting energy firing the boiler.

Do you agree?

 

[Dan Robinson]

Try lowering the P:b setting.


Have you measured the waste of gas? Otherwise it is subjective.

 

[ALEC1]

TPI was developed to work with bus communication which lowers the boiler temperature as the room temperature rises. Because we steadfastly refuse to adopt this technology in the UK manufacturers mixed it with a simple relay which turns the boiler on and off around a set point, the boiler thermostat. Instead of lowering the flow temp around target room temp, it cycles the boiler, holding it off to lower the average temperature of the rads.

Really you should be monitoring room temperature...not the boiler activity.


Like anything if you use it as the designers intend then it will be issue free, but if you modify slightly then there is a down side...amd you have just discovered it!

 

[Dan Robinson]

Dude. ..really? He's got an on/off boiler. This is fine other than the risk of condensation on the cast hex.

 

[ALEC1]

no, the OP cannot do anything about the way his TPI interacts with the boiler..unless he changes both the boiler and the sat, some thing that won't be happening.

But its a good example of the way manufacturers pull the wool over everyones eyes to sell substandard technology to make money...frustrating on several levels, not least because if the manufacturers gave us more information then we could install heating systems that behave as expected...

as ever the installer picks up the pieces...and some even defend the manufacturers!

 

[Dan Robinson]

Wild accusations do not a case make .

According to a recent post you made in the other place my system shouldn't function let alone condense yet I have about 2 gallons a day of condensate to get rid of. And a boiler that sits in a fully condensing state for nearly all its operating life.

Granted my controls are not tpi, but the Evo implementation of some form of fuzzy logic. Still on/off though.

 

[ALEC1]

Dan I have never said that your system should not condense...

at the end of the day an average low flow temperature will enhance efficiency...but the cycling produced by tip strategies may loose that... ( unburnt gases and the fan cooling the heat exchanger for example..)

 

[Dan Robinson]

Your exact words were "All systems on on-off controls will only condense on startup".


Search the cc for "2 gallons" and it is the 3rd answer. Links in nicely with my turndown ratio shenanigans