Modulating Boiler Controls

[df55555]

We have just had a Remeha 35c installed and it was connected to our existing Honeywell cm927 stat, that previously controlled an old Biasi boiler.

The boilers fine - plenty of hot water hot radiators, no problem there. We do notice that the house gets, I won't say cold, but chilly. The stat in the hallway reads room temp at 21c, other thermometers confirm this is the case in most other rooms as well. But The radiators are always mostly cold, the house is very well insulated, walls loft, double glazed throughout - so I'm assuming it heats up quickly maintains temperature well & the boiler doesn't need to do much once we are up to temperature.

I've read a lot on here & elsewhere about modulating controls and that they operate the boiler at lower output - seems to benefit in gas costs & room comfort. I've also seen that the honeywell opentherm wireless stats aren't available in the uk. We want a modulating control - but we also want to set day & night temperatures, which means a programmable controller. Running a cable isn't an option any more - if we have to have wired - then the controller needs to live by the boiler.

Is there anything out there that would work for us at the moment ?

 

[bengasman]

Move the stat to the lounge; location in hall is how it was done in the 60's

 

[df55555]

We've done that - it can clip off of the wall & be put on a stand in the living room. - doesn't make any difference.
The hallway radiator is the only one without a trv & seems a sensible place to set the temperature. We then reduce the rtv's in each room that needs it to get an even temperature house wide.

What we are trying to do is find a modulating controller that works for us to get the most out of the boiler. Running for longer periods at lower flow temperatures will hopefully make for a more even temperature 'feel'.
It's a bit weird as the stats all say the house is at 21c - but theres definitely something not quite right. It we keep the boiler closer to condensing mode then we also save a few quid hopefully.

This I found an interesting read - wikiclimate.net/wiki/Condensing_Boiler_efficiency

 

[bengasman]

Let's get back to the start.

What is your primary goal?
Bear in mind that in a lot of cases like this where people want 4 things at the same time, one or two will not be compatible.

No disrespect, but as you are not a heating engineer, it appears you are trying to match you "problem" to the solution you have chosen.

What exactly do you mean by "modulating control"?

 

[df55555]

Our main problem is that although the room stat states 21c as does a thermometer in each room - that there are cold spots or the room is perceived to be chilly.

We also have just had a condensing boiler fitted - so we'd also like to control it in a way where we get the most out of it. An on/off stat isn't using the boiler efficiently - it's off for long periods then on at 100% output briefly. I think this is whats really causing the cold spots. The old screwfix boiler would be on loads as it worked hard to work heat the house up - so the rads always had some heat in them.

Any product that seems to fit the bill isn't available in the uk yet - remehas isense rf or the honeywell opentherm stats.

 

[bengasman]

Our main problem is that although the room stat states 21c as does a thermometer in each room -

Forget what it says, as neither is calibrated, it is only an approximation.

that there are cold spots

Controls won't change that

or the room is perceived to be chilly.

Turn the temp up 2 degrees, or wear a woollie; controls have nothing to do with that.

We also have just had a condensing boiler fitted - so we'd also like to control it in a way where we get the most out of it. An on/off stat isn't using the boiler efficiently - it's off for long periods then on at 100% output briefly.

No control will change that unless you completely alter the setup to weather compensation.
The average difference in your gasbill will be about 2% compared to a normally controlled balanced system. Besides that, your assumption that the boiler will come on at 100% is wrong too.

I think this is whats really causing the cold spots.

Wrong

Any product that seems to fit the bill isn't available in the uk yet - remehas isense rf or the honeywell opentherm stats.

As above, only full change to weather compensation will effect the boiler, but still do nothing about the cold spots or perception of chill.

 

[Agile]

Our main problem is that although the room stat states 21c as does a thermometer in each room - that there are cold spots or the room is perceived to be chilly.

In that case you need to fit a fan to distribute the air around the room.

There are nice ceiling fans at B&Q !

Tony

 

[JohnD]

but this might also happen if there are draughts, or if the house has not been heated long enough for the walls to become evenly warm; or if you have areas of high heat-loss, such as a conservatory, large windows or solid external walls, or damp patches, or you leave the internal doors open. These problems are not so common now, but in previous times it was quite common to have a large room, roasting round the fireplace but cold in the far corners. If the heating is off for long periods, and the fabric of the house becomes cold, then the radiators will warm the air first, and that will slowly heat up the walls. This will give a sensation of chill even though the thermometer tells you the air is warm.

Bare downstairs floors in particular are draughty and much colder than carpets

BTW I now have a modern modulating boiler, and oversized radiators, so unless the weather is very cold I can leave the boiler stat set to 60C, and it just ticks along keeping the radiators warm. In very cold weather I have to turn the boiler stat up so it heats the house quicker from cold (oversized rads are very good for this, but it is no so necessary now I have a programmable room stat.)

 

[ianniann]

No control will change that unless you completely alter the setup to weather compensation.

Weather compensation and boiler (temperature) modulation are two completely separate things. Please can everyone stop spouting "weather compensation" as if it is the only way to control the flow temperature of a boiler.

 

[JohnD]

Please can everyone stop spouting "weather compensation" as if it is the only way to control the flow temperature of a boiler.

Who is this "everyone"?

 

[df55555]

Well thanks for all your comments, even the ones that seem to be only to disagree.

This isn't my trade but I've been asking a Dutch heating engineer who works in my building, he works on commercial systems but he does have some domestic experience.

He seems to think it's less than ideal we have regulations that enforce condensing boilers then don't fit controls to make them operate efficiently. As I understand it the stat as I know it becomes a sensor to supply information to the boiler - which then uses that to adjust the flow temperature to achieve the desired room temp. You can also add an external sensor that will have some effect on temperature & timing, but room stats are probably all thats needed in my case. The savings come from the boiler operating more efficiently at a lower temperature - which has a side effect of being gentler on the boiler & more likely to achieve a constant room temp.

At the moment the Honeywell & the Avanta just don't seem to be working properly together - I understand that when something changes, it takes a while to get used to the new system, but something ain't quite right. The old boiler was on it's way out - but seemed to achieve a better constant room temperature. The hot water flow rates a resounding sucsess, I just can't seem to find a balance that works.

 

[JohnD]

what was your gas usage in the last 12 months, what was it in the preceding 12 months?

Was your house equally warm? Did you alter the room stat settings or timings?

What date was the boiler installed?

edited:
some very important questions
Are your radiators correctly balanced?
What is the output capacity of all the radiators that you have turned on?
I understand your new boiler is rated at 35kW, was your old boiler 15kW or what?
Do you have reason to believe that your new boiler does not modulate its output according to load? It is supposed to range between 6-31.3kW
(I am an informed householder, not a pro)

 

[bengasman]

No control will change that unless you completely alter the setup to weather compensation.

Weather compensation and boiler (temperature) modulation are two completely separate things. Please can everyone stop spouting "weather compensation" as if it is the only way to control the flow temperature of a boiler.

If there is another way of influencing the flow temp without human intervention I'd most oblige if you could enlighten me.

 

[dumbrill]

At the moment the Honeywell & the Avanta just don't seem to be working properly together - I understand that when something changes, it takes a while to get used to the new system, but something ain't quite right. The old boiler was on it's way out - but seemed to achieve a better constant room temperature. The hot water flow rates a resounding sucsess, I just can't seem to find a balance that works.

My own experience of an Avanta 18S and a CM927 also suggests that they don't work particularly well together. Neither however is the control really bad.

The CM927 cycles the boiler on and off so many times an hour and this can't be as efficient as running the boiler for longer on low power.

My thoughts were that the CM927 simulates modulation by cycling the boiler on an off and so is really best suited to an old style boiler that operates at 100% or nothing. However the Avanta doesn't (always) operate at full power. I assume it probably tries to optimise the flow and return temperatures, but the end result is a boiler that varies it output and a thermostat that doesn't have any 'knowledge' of what the boiler is doing.

I used the CM927 for about 4 weeks with my new 18S whilst waiting to fit an iSense. With the iSense fitted the boiler stays on for much longer with no cycling and it produces a lot more condensate.

My comments are nothing to do with weather compensation because the performance of the iSense is still better when used as a simple modulating room stat.

In your case I assume that the results would be much the same for the 35C as it shares the same controls, etc. The simpler alternative to the iSense is the Celcia, but I'm not sure whether the Celcia can be used without an outside sensor as a simple modulating stat.

I would choose the iSense again and it has a very nice user interface, but the wireless version is going to cost you +£200 and you'll have to buy it from abroad.

 

[dumbrill]

I should add that the CM927 worked very well with my old Glowworm Hideaway for 5 years or more.