Discuss Central Heating and the modulating boiler. in the Central Heating Systems area at ElectriciansForums.net

EricMark

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To start with it all seems to make sense, the TRV measures the room temperature and controls the radiator temperature to suit, as the water flow is restricted the by-pass valve lifts, and hotter water is returned to boiler, so the boiler is throttled back (modulated) so the heat exchanger is cool enough to keep the flue gases below the critical temperature where moisture will condense out of it. Until the point where the boiler can’t be modulated any more, at which point the boiler will start to cycle, there may be anti-cycle software which if on switch on the water returns hot will extend the off time, and if not reduce off time, however it can’t ever switch completely off, as there is nothing then to kick start it into running again. That is OK can understand it so far.

But then we get into the muddy area, it would seem what we need is for the wall thermostat to simply kick-start the boiler, so when wall thermostat is satisfied the boiler will remain stopped, and when wall thermostat shows a demand it will run again until it reaches minimum output again. If while boiler is running and the thermostat is satisfied, it will continue to run, as the wall thermostat is only in one location, and other locations must require the boiler to run or the return water would be hot and it would auto turn off.

However this is not the case, when the wall thermostat is satisfied, the boiler turns off, even if still at maximum output.

To my simple mind there should be two inputs to the boiler, time clock and wall thermostat, the time clock will switch the boiler both on and off, the wall thermostat will only turn it on.

Since this does not happen, I have clearly got it wrong, so can some kind sole take the time to explain how a wall thermostat is installed to stop boiler cycling without it switching off boiler prematurely? Especially with programmable TRV heads.

On another thread it was suggested a number of ways to sense when boiler is fully modulated, however I would not have expected to need to add gas flow switches or other sensors, I would have expected this to be already built into the boiler.
 

Lucien Nunes

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I agree that the room stat is a bit of an anomaly these days. Historically, before TRVs, it could regulate temperature if the heat input to each room was set correctly relative to the heat input to the area sensed by the thermostat, to give appropriate temperature rise throughout. With TRVs, proportional control using the room stat's accelerator heater to cycle the boiler no longer served so much of purpose, as the TRVs would react inversely to changes in average flow temp and hence rad output resulting from the room stat duty cycle. So in a way it was already demoted to just triggering the system when the average room temp was low and the system was idle. Modulating boilers just make yet more redundant.
 

PEG

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Yep,the increase of additional ideas and systems,to what is basically,a method of heating,the Romans had,has not made design and set-up,an easy proposition.

Exactly the same problem exists,with our vehicle job,where euro 6 cat's,dpf's,scr's and adblue...are nailed on to what are essentially a 70 year old design of CI combustion engine :cool:
 
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EricMark

EricMark

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Yep,the increase of additional ideas and systems,to what is basically,a method of heating,the Romans had,has not made design and set-up,an easy proposition.

Exactly the same problem exists,with our vehicle job,where euro 6 cat's,dpf's,scr's and adblue...are nailed on to what are essentially a 70 year old design of CI combustion engine :cool:
The big difference, one manufacturer selects what goes in each car, the central heating we have loads of different manufacturers all claiming their bit is the best since sliced bread, and some times they simply don't work together. I like the idea of OpenTherm where you should in theory be able to mix and match. However every report you read seems to have a different idea on how well it works, and with internet you often have no idea how long ago the report was written.

I have slated Hive as hot water version is not volt free, it does not have OpenTherm and it has no TRV's which link, however today it does have TRV heads that work with it, although have to watch which version one is using, but I am sure comments I made before the £80 TRV heads were released are still on the net some where.

I still see reports on how you should not fit a TRV in same room as wall thermostat, but today the wall thermostat can be linked to the TRV head so that no longer hold true.

However there are always stick in the muds, who still top up the dash pots on motor starters!
 
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PEG

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Hi,one manufacturer does not make the extra emission kit,for each vehicle.

Most of it,is as generic as central heating parts. There are six wagon makers,all using the same SCR's,adblue pumps and Nox sensors.

I suppose the difference is,that no vehicle manufacturer will countenance or advise,any other bits and diagnosing,than strictly their own. Whereas,every manufacturer of central heating components,knows for a fact,it will be working with a group of foreign friends;)

How many condensing boilers,are out there,working out of their condensing range,due to system designs,and customers expectations? It certainly is possible...but not without having the inside corners of all your pockets,full of Celotex :cool:
 
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EricMark

EricMark

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I will have to admit mine had a stupid selection of thermostat, the Honeywell Y6630D wireless thermostat is very good, it has fail safe built in, and anti hysteresis software, so as it gets near to target temperature it starts a mark/space ratio so it does not over shoot. However that completely messed up the boilers modulating features.

I hunted for a wireless thermostat with fail safe, so if signal lost it auto closed down, but without the anti hysteresis software, and simply could not find one. All I wanted thermostat to do was turn off heating on a warm day, it was not there to control the temperature of the hall, the TRV with an Energenie MiHome electronic head would keep to hall to within 0.5 degrees to the temperature set, it worked very well, also had three more around the house.

I will admit the lock shield had to be carefully set, as it takes time for the motor to adjust the valve, and if not throttled back with lock shield valve rad gets hot before valve has time to close.

I found once lock shield set even the mechanical valves worked well, however *123456 does not really help, what was wrong is marking in degrees C?

I read up on how boiler worked, I had a bosch Worcester and it seemed they did their own modulating thermostat called wave, but then found my boiler was an early model and it would not fit. The TRV heads were designed to work with Nest, however since bosch Worcester not OpenTherm it would have to use on/off control and like the Honeywell Y6630D it had anti hysteresis software so would start switching boiler on/off using a mark/space ratio.

Then moved house, no gas just oil, and it seems oil boilers don't modulate so the oil bosch Worcester works fine with Nest set to switch on/off with mark space ratio. However the pairing of Energenie with Nest seems odd, the Energenie software controls Nest which in turn tells the TRV head what temperature is set, is that not the wrong way around? I thought the TRV should tell the main thermostat when it wanted hot water, not the other way around?

So what is the point in having a £40 TRV head, OK I can change temperature anywhere in the world, but really don't care what the house temperature is when I am not at home. So for £10 I can buy electronic heads and can set a schedule, actually paid a little more and got Bluetooth model so don't need to crawl on the floor to read display, but still only £15 each.

So now looking at daughters house, it's OK if I get it wrong with my house, my money, but daughters house, want it right first time. Using my logic skills, what needs to happen is the boiler says can't modulate any more I'm turning off, and then the thermostat takes over and when the room cools it tells boiler OK your needed again turn on. So the boiler would have two independent connections, one for thermostat, and one for timer or on/off switch. However that does not seem to be the case.

Am I going mad?
 

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