So your system isn't balanced, then. Also completely ignored all of my previous questions. The flow temperature should not have an effect like that, but if you're happy wasting your money on unecessary gas then you go ahead.
How to optimise your combi boiler
- Thread starter dirtychinchilla
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Soldato
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Is it?Boiler performing well this morning.
Why is the flow temp spiking by such a small amount over such a small time period, without much of a change over the return temp?
Are you not reading the graph correctly the temp is going from like 30c to maybe 35c when the flame comes on even my high modulating boiler has its limits so it's cycling. Small increase in room temp and only two rooms.
Soldato
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Boilers aren't supposed to cycle though, it's inefficient. Most (if not all) have an inbuilt anti cycle delay of 4 to 20 mins. It's better to modulate rather than short cycle.
Raising the flow temp by 5C at the source for only 30 seconds (if that graph is right), will not do much to the air temp of a room by the time that small pocket of heat has left the boiler, gone down the pipes, reached the radiator, and then convected into the air in the room. Would it actually accomplish anything apart from using gas with not much benefit?
I would have expected to see that graph show a steady line increasing away from the return temp, keeping around 20C difference to maximise condensing efficiency.
Edit: Even Honeywells own evohome system short cycles the boiler for 5 minutes at a time for around 2 weeks after installation, while each radiator trv learns how much is needed from the boiler to make a change to the temperature in each room to maintain/reach its set point, without over or under shooting.
Raising the flow temp by 5C at the source for only 30 seconds (if that graph is right), will not do much to the air temp of a room by the time that small pocket of heat has left the boiler, gone down the pipes, reached the radiator, and then convected into the air in the room. Would it actually accomplish anything apart from using gas with not much benefit?
I would have expected to see that graph show a steady line increasing away from the return temp, keeping around 20C difference to maximise condensing efficiency.
Edit: Even Honeywells own evohome system short cycles the boiler for 5 minutes at a time for around 2 weeks after installation, while each radiator trv learns how much is needed from the boiler to make a change to the temperature in each room to maintain/reach its set point, without over or under shooting.
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20c drop at 30c okay, you sound like you know your stuff. All boilers cycle at their limit, modulation isn't unlimited there is a minimum and maximum, the scenario this morning is clearly below the minimum.
Opentherm requests a temperature the boiler is doing it's best to deliver it.
The graph for the first 10 minutes did indeed have a nice long going up from 16c or so up to the requested 35c then it shut off and dropped, to 30c then it cycled to maintain that temp.
If the demand was higher but also for 35c the boiler would be able to stay on and hold a steady 35c. On the middle of winter I've seen it hold 23c constantly for hours just ticking away at its lowest modulation. Its not cold enough for that yet though.
My Evohome settings are 6 per hour at 2mins. As per the boiler manufacturers recommendation.
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Still haven't had my heating come on as I have had the thermostat set to 17c
Really don't want a 3k energy bill.
Problem is with 65c is that it won't put the boiler in condenser mode, which is where the real economy is.
Return temperature below 55C is what you need. The flow temperature only matters because you want a high dT.
Soldato
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Definitely weather compensation helps a lot but mornings like today where it's generally cooler than the setpoint the whole day the heating comes on but at it's least efficiency.Start of season oddities
Off to look at 5 boilers now, no rest for the wicked!
Once the rooms need a constant input of energy to maintain a temperature the boiler status on much longer.
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A lot of boilers are massively oversized for the heating side usually due to them being a combi and needing the max power to heat the hot water. For efficient heating you want a boiler that can modulate down to 1-3kw that means it can run a couple of large ish radiators without cycling.
I found I use less gas by running a higher flow/return than lowering it and allowing the boiler to cycle. My heating was on this morning return was 34c and it ran for 2 hours without cycling if I try and lower the heating curve and get the return under 30c it starts to cycle using more gas.
When my boiler needs replaced I will make sure I get one that can modulate as low as possible. It wasn't something I took into account when getting the system replaced as I needed the higher output to run the system on the coldest days. Mine only drops to 6kw but a Viessmann 200-W has a 17:1 modulation ratio and can go down to 1.8kw while offering the same maximum output as mine.
I found I use less gas by running a higher flow/return than lowering it and allowing the boiler to cycle. My heating was on this morning return was 34c and it ran for 2 hours without cycling if I try and lower the heating curve and get the return under 30c it starts to cycle using more gas.
When my boiler needs replaced I will make sure I get one that can modulate as low as possible. It wasn't something I took into account when getting the system replaced as I needed the higher output to run the system on the coldest days. Mine only drops to 6kw but a Viessmann 200-W has a 17:1 modulation ratio and can go down to 1.8kw while offering the same maximum output as mine.
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My 32kw does max 28kw and min 4.7kw.
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I thought you could actually plot flame on/off to distinguish if boiler is cycling - from some of the opentherm plots I've seen,
since otherwise yes if you are short cycling you have the additional gas consumption from housekeeping/clean-up as it turns off
since otherwise yes if you are short cycling you have the additional gas consumption from housekeeping/clean-up as it turns off
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If anyone is interested I have a Nest thermostat, wired over a standard switching input to a modern combi (not opentherm) fitted with an outdoor weather sensor.
My boiler is set to run heat curve 25: Cos I don't like being cold
For an Example:
Monday this week used 24.3KWh of Gas, which included the Heating and multiple showers and any other hot water usage in our house. And cost £2.77 according to our smart meter.
The Nest ran the heating for a total of 4.75Hrs on Monday to maintain the program below. And according to a quick internet search the outside temp for Monday ranged from 6C up to 17C for our location.
According to MoneySavingExpert website, our annual energy consumption is above average, but in all honesty I'm quite happy with how efficient our system is and will run it to be comfortable thankyouverymuch
Edit: The biggest issue in our house is the conservatory, its just a standard build and so bleeds heat when the outside temperature drops (lovely in Summer though), and we leave two big doors open to it and use the space just like any other room. We could save a tonne of gas if we didnt have the conservatory, but heyho it is what it is.
My boiler is set to run heat curve 25: Cos I don't like being cold
For an Example:
Monday this week used 24.3KWh of Gas, which included the Heating and multiple showers and any other hot water usage in our house. And cost £2.77 according to our smart meter.
The Nest ran the heating for a total of 4.75Hrs on Monday to maintain the program below. And according to a quick internet search the outside temp for Monday ranged from 6C up to 17C for our location.
According to MoneySavingExpert website, our annual energy consumption is above average, but in all honesty I'm quite happy with how efficient our system is and will run it to be comfortable thankyouverymuch
Edit: The biggest issue in our house is the conservatory, its just a standard build and so bleeds heat when the outside temperature drops (lovely in Summer though), and we leave two big doors open to it and use the space just like any other room. We could save a tonne of gas if we didnt have the conservatory, but heyho it is what it is.
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Soldato
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Really chuffed with my boiler now:
Radiators all balanced so they return about 70% of their input temperature (yes, I realise the return here is about 50% of the output, but the input temps are about 50'C according to FLIR, whereas these temperatures are thermal probes at the boiler itself, and I'm not 100% certain of their calibration, or the accuracy of the FLIR).
Boiler pump set to speed 1 instead of 3 (it only has a simple pump with three speed settings).
Radiators all balanced so they return about 70% of their input temperature (yes, I realise the return here is about 50% of the output, but the input temps are about 50'C according to FLIR, whereas these temperatures are thermal probes at the boiler itself, and I'm not 100% certain of their calibration, or the accuracy of the FLIR).
Boiler pump set to speed 1 instead of 3 (it only has a simple pump with three speed settings).
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Soldato
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Wow, are you paying only 11.4 p per kWh of gas?
We're on around 14.3p after the October price rises (roughly - we pay a different rate for the first 2000 kWh, so this is my estimate).
so should we infer it is a modulated output down at 20C , say, outside of evening slot ... will the boiler report modulation level ?
I'm thinking of some of the opentherm plots I'd mentioned earlier via
eg.
Soldato
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Just checked and according to our smart meter we are paying 10.236p Inc vat
Soldato
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No, that's with the heating off.
Switched it on about 18:00 and off about 22:30.
It might report modulation levels, but I'd need to go into the status on the boiler itself.
It's a 7 year old Worcester Bosch Greenstar 30Si Compact. The manual doesn't say what the min modulation is on the heating (24 kW), only the water (7 - 30 kW)
The plots are my own thermal probes running from a Raspberry Pi zero.
Have people put their heating on yet? We have a new apartment and the temperature remains between 22 and 23.5C all day and night. Not had the heating on since we move in, other than to confirm it works a few weeks ago.
Most days we hit about 23.5c late afternoon and then about 9 am are around 22.1c, before we seem to warm again we have a very large south facing window, 4.5m x 2.2m and I am thinking we are being heated by this during the day
Most days we hit about 23.5c late afternoon and then about 9 am are around 22.1c, before we seem to warm again we have a very large south facing window, 4.5m x 2.2m and I am thinking we are being heated by this during the day
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you live in the UK and your house is holding 20C at the moment .. I'm in a <10 year old place, yes - windows have been open during the day, and kitchen whilst cooking, but it's 17C in the hall.
e: trickle vents aren't closed otherwise it'll be stuffy, equally bedroom windows open a jar at night time.
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