Non-Condensing Boiler Flow Temperature?

paperclap
paperclap Posts: 671
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Hi all,

We’ve an old non-condensing conventional Potterton Profile 40e boiler.

In a bid to save a bit of money, I had planned to turn down the flow temperature on the boiler.

But, is this wise to do on a non-condensing boiler? I’m no expert, but from what I’ve read, if the flow temperature is too low on a non-condensing boiler, if can cause corrosion?

Our boiler has settings 1, 2, 3, 4, 5 and Max.

According to the manual, this is 55°C-82°C.

This would mean:
1 = 55°C
2 = 60.4°C
3 = 65.8°C
4 = 71.2°C
5 = 76.6°C
Max = 82°C

It is currently on 5.

With this in mind, is there a minimum setting I should go to, where I can cause no corrosion on the boiler, but save money in the process?

Thanks!
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  • BUFF
    BUFF Posts: 2,185
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    edited 12 December 2022 at 10:11PM
    it likely won't make any difference in efficiency.
    You are told to do so on a condensing boiler because it recovers additional energy from the exhaust gases by condensation & the cooler that you can run the return the more energy it will recover - this is not relevant for a non-condensing boiler.

    p.s. fyi your boiler had an efficiency of 71.8% when new
  • macman
    macman Posts: 52,955
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    And probably a lot lower some 20-odd years later.
    No free lunch, and no free laptop ;)
  • Don’t disagree with either of you!

    But, the cost of a new boiler is a pretty penny. 

    The efficiency (and therefore the cost savings) of a new boiler would be less than the cost of the new boiler.

    Therefore, economy more wise to actually keep the older, inefficient boiler.
  • housebuyer143
    housebuyer143 Posts: 3,167
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    edited 13 December 2022 at 7:24AM
    paperclap said:
    Don’t disagree with either of you!

    But, the cost of a new boiler is a pretty penny. 

    The efficiency (and therefore the cost savings) of a new boiler would be less than the cost of the new boiler.

    Therefore, economy more wise to actually keep the older, inefficient boiler.
    I'm thinking along the same lines as you. 20 yr old non condescending boiler. I am told the best saving I will make it £500 a year by changing it, based on the new tariffs (I am currently paying less than half of this, so saving is more like £200).
    New boiler is £3500, so worst case it would take 7 years to recoup the cost. 
    My boiler isn't as efficient as it could be but it's cheaper to keep it. 

    In answer to your question, British gas advised me you save almost nothing turning it down. However what will happen if you turn it to less than 65-70 is that your hot water tank won't heat up very hot, if you have one 
  • ThisIsWeird
    ThisIsWeird Posts: 4,458
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    This is an interesting question. In theory, the cooler you run the boiler's water temp - ie the cooler the heat exchanger casing will be -  the more heat it will extract from the burner. This is regardless of whether the boiler is a condensing on non-condensing type.
    This will ned to be balanced against whether a cooler temp will then heat the radiators enough to warm the house, and possibly more importantly, whether it'll heat the hot cylinder enough to be safe too.
    That boiler has a cast iron heat exchanger, so I'd imagine it's pretty corrosion-resistant, and Pottereton wouldn't provide that range of output temps in any case if there was a risk of their boiler failling apart from rust if run at 1, 2 or 3. This is what they say:
    "Boiler Thermostat
    The boiler thermostat enables you to control the
    temperature of the water as it leaves the boiler and is
    also used for turning the boiler on and off. The thermostat
    knob can be set between 'O' (OFF), 1, 2, 3, 4, 5 or Max.
    The graduations 1 to MAX correspond approximately to
    a temperature range of 55 °C to 82 °C
    During the summer months, when the boiler is only being
    used to supply stored domestic hot water and there is no
    independent hot water temperature control, the
    thermostat can be set to position 1 or 2 which will
    probably be hot enough for bathing or washing up
    requirements. For washing clothes a higher setting may
    be necessary.
    In winter weather, when central heating is required, the
    thermostat knob can be turned up higher but it must be
    remembered that unless the temperature of the water in
    the domestic hot water cylinder is independently
    controlled, the stored hot water could be at a temperature
    that could scald."
    Provided the temp is still high enough to heat your home, paperclap, I think I would try lowering it down a touch to 4 or fractionally under. It might save you a %, maybe even %%, but it should also reduce the overall strain on the boiler and hopefully help eke it out for a few more years until you decide what the next heating system should be.
    Although energy costs have soared, and the argument for changing to high-efficiency boilers is therefore possibly stronger, I think it still makes more sense to hold off as long as possible if only to see what possible new types of heating systems become available, or even if better energy grants come along to support them. For the majority of the UK's houses, ASHPs, for example, are surely not going to do the job unless accompanied with extensive added insulation? And many home owners won't be able to pay for this out of their own pockets.
  • ThisIsWeird, this is great, thank you!

    Today, as we speak, I'm running a little experiment. Central heating on all day. Thermostat set to 18 degrees. Boiler setting at 5. All radiator TRVs are set to Max.

    Going to see how much on average, per hour, it costs.

    Then on Thursday, I'll do the same text. But, drop the boiler setting to 4. And maybe, the TRVs to 5 or 4, too.
  • FreeBear
    FreeBear Posts: 14,251
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    Keep an eye on the temperature outside.
    If there is a huge variation, that is going to throw a (small) spanner in to any comparisons you try to make - Not that I think it will make much of a difference.
    Her courage will change the world.

    Treasure the moments that you have. Savour them for as long as you can for they will never come back again.
  • Both days are 2 degrees during the day... and around -1 at night!

    So hopefully a relatively good comparison.
  • macman
    macman Posts: 52,955
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    paperclap said:
    Don’t disagree with either of you!

    But, the cost of a new boiler is a pretty penny. 

    The efficiency (and therefore the cost savings) of a new boiler would be less than the cost of the new boiler.

    Therefore, economy more wise to actually keep the older, inefficient boiler.
    No, because each year you retain the old, inefficient boiler, you are spending more on gas than you need to. The only variable is the length of time it will take to recover the capital outlay in gas bill savings. This will depend on a) the amount of gas you use each year, and b) the unit price of gas. 
    One thing is certain: with the near-tripling of gas prices, the payback time will be much shorter than a year ago. If it was a decade last year, then now it will be maybe 3 years. And then we can expect a further 27% increase in April, so the argument for a new efficient boiler now is even stronger.

    No free lunch, and no free laptop ;)
  • macman
    macman Posts: 52,955
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    edited 13 December 2022 at 1:10PM
    paperclap said:
    Don’t disagree with either of you!

    But, the cost of a new boiler is a pretty penny. 

    The efficiency (and therefore the cost savings) of a new boiler would be less than the cost of the new boiler.

    Therefore, economy more wise to actually keep the older, inefficient boiler.
    I'm thinking along the same lines as you. 20 yr old non condescending boiler. I am told the best saving I will make it £500 a year by changing it, based on the new tariffs (I am currently paying less than half of this, so saving is more like £200).
    New boiler is £3500, so worst case it would take 7 years to recoup the cost. 
    My boiler isn't as efficient as it could be but it's cheaper to keep it. 

    In answer to your question, British gas advised me you save almost nothing turning it down. However what will happen if you turn it to less than 65-70 is that your hot water tank won't heat up very hot, if you have one 
    If your quote for £3.5k was from BG, then you can expect to pay 40% less from a local GSR RGI. BG typically quote 40% over market rate for a new install, so the going rate would be £2k to 32.5K, unless your system is atypical. So, given current rates and a further c. 27% rise coming in April, the payback time might be a lot less than 7 years, depending on your usage. 
    What is being discussed being turned down is the flow temp, not the temp on your hot water tank. This only applies to condensing combi's, not conventional boilers like yours. The temp on your hot tank is controlled by the 'stat fitted to the tank, not by the boiler.
    BTW, my boiler is only 5 years old, and it's also non-condescending...
    No free lunch, and no free laptop ;)
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