Leaking cylinder, time for a combi boiler?

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  • LuxxmanLuxxman Frets: 36
    Lots of people are changing over to combi's, but if you ever decide to get PV's installed on your house the most efficient way you can use the energy you generate is by heating hot water in a (well insulated) cylinder using a small (relatively cheap) thing called an Immersun. Storing energy in hot water is more efficient than storing energy in a Tesla battery as we are finding in the EU Community Energy project I am involved in in Nottingham.
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  • quarkyquarky Frets: 2777
    ICBM said:
    I have never been in a house with any kind of on-demand water heating that works as well as one with a good old-fashioned gravity fed hot water tank system.

    If you’ve got a tank system and the tank is leaking, just replace the tank - it’s both the easiest and the best solution.

    Thanks. The thing is, I have a weird tank where the HW and CH are together, so even when the CH is off, I assume it must still be drawing *some* heat. I have a copper tank which is not done any more, but apparently a stainless steel tank is an option..

    Luxxman said:
    Lots of people are changing over to combi's, but if you ever decide to get PV's installed on your house the most efficient way you can use the energy you generate is by heating hot water in a (well insulated) cylinder using a small (relatively cheap) thing called an Immersun. Storing energy in hot water is more efficient than storing energy in a Tesla battery as we are finding in the EU Community Energy project I am involved in in Nottingham.

    That is a really good point. I have a dormer on the south facing roof so that is unlikely in the short term, but possible when solar panels are smaller/lighter I guess.

    axisus said:
    quarky said:
    We have about five bedrooms, three bathrooms, and there are four of us. Two adults, and two kids
    Wow, how the other half live! We have 2 and a half bedrooms, 1 bathroom and there's 6 of us! 
    I have to move a *long* way from work to get it though!
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  • FretwiredFretwired Frets: 24601
    @quarky - what part of the world do you live in? What's the water like?

    Remember, it's easier to criticise than create!
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  • quarkyquarky Frets: 2777
    Northamptonshire. Very hard water, but my water pressure is very high too.
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  • FretwiredFretwired Frets: 24601
    quarky said:
    Northamptonshire. Very hard water, but my water pressure is very high too.
    OK - my son lived in a hard water area and had lots of problems with his combi boiler. If you decide to get one fit a scale inhibitor or water softener.

    Remember, it's easier to criticise than create!
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  • danodano Frets: 1568
    Luxxman said:
    Lots of people are changing over to combi's, but if you ever decide to get PV's installed on your house the most efficient way you can use the energy you generate is by heating hot water in a (well insulated) cylinder using a small (relatively cheap) thing called an Immersun. Storing energy in hot water is more efficient than storing energy in a Tesla battery as we are finding in the EU Community Energy project I am involved in in Nottingham.
    Very intereting.  Have you a link to any reading material on this? I guess your username is based on lux from the sun ?!
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  • chillidoggychillidoggy Frets: 17136
    edited January 2018
    Combi boilers are not good in hard water areas unless you fit a water softener. My mate had one, it lasted a year before it was so furred, it was unusable.

    Oh, and if you fit one, you lose the airing cupboard, which would be grounds for a kick in the bollocks, followed by a divorce, in my gaff.


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  • exocetexocet Frets: 1948
    quarky said:
    ICBM said:
    I have never been in a house with any kind of on-demand water heating that works as well as one with a good old-fashioned gravity fed hot water tank system.

    If you’ve got a tank system and the tank is leaking, just replace the tank - it’s both the easiest and the best solution.

    Thanks. The thing is, I have a weird tank where the HW and CH are together, so even when the CH is off, I assume it must still be drawing *some* heat. I have a copper tank which is not done any more, but apparently a stainless steel tank is an option..

    Luxxman said:
    Lots of people are changing over to combi's, but if you ever decide to get PV's installed on your house the most efficient way you can use the energy you generate is by heating hot water in a (well insulated) cylinder using a small (relatively cheap) thing called an Immersun. Storing energy in hot water is more efficient than storing energy in a Tesla battery as we are finding in the EU Community Energy project I am involved in in Nottingham.

    That is a really good point. I have a dormer on the south facing roof so that is unlikely in the short term, but possible when solar panels are smaller/lighter I guess.

    axisus said:
    quarky said:
    We have about five bedrooms, three bathrooms, and there are four of us. Two adults, and two kids
    Wow, how the other half live! We have 2 and a half bedrooms, 1 bathroom and there's 6 of us! 
    I have to move a *long* way from work to get it though!
    Sounds like you have what is known as "Gravity Fed Hot Water". I thought this type of system went out of fashion in the 70's. Basically this system has no valves to direct the flow from Hot Water / Heating or both. The boiler fires up, which heats water in the HW tank. If you want heating - the pump kicks in to circulate around the radiators but you can't separate the HW if the radiators are on. If you have the heating on for many hours, the HW gets extremely hot!

    No reason why you can't replace with standard boiler and update the tank and heating controls at the same time. Stainless Steel tanks are available but more expensive. 
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  • exocet said:
    Basically this system has no valves to direct the flow from Hot Water / Heating or both. The boiler fires up, which heats water in the HW tank. If you want heating - the pump kicks in to circulate around the radiators but you can't separate the HW if the radiators are on.
    Easiest way to check for the switching is to look for a metal box about 5 x 2 X 2 inches with junction to three pipes and an electric cable. That's a motorised valve to switch between HW/CH so it's all separated.
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  • We recently changed from  a traditional cylinder/tank system to a combi, loving it so far! Shower is off the bath taps and is so much more powerful now. No problems with supply vs demand so far. Heating seems more efficient, and I am expecting to use barely any gas in summer, other than showers. 

    this is in a 3 bedroom 1 bathroom house with two of us. 

    Cost us 2300 including rerouting gas through a bigger pipe and a new radiator.
    I'm just a Maserati in a world of Kias.
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  • quarkyquarky Frets: 2777
    This is the existing boiler here. Now I am worried about being in a hard water area. :/ 

    https://1drv.ms/i/s!An1C7f0Qk0d1jpNv_foNlp_QqL_D8g

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  • quarkyquarky Frets: 2777
    edited January 2018
    This is the recommended one. 
    http://www.directheatingsupplies.co.uk/ideal-logic-plus-35-combi-boiler
    Or a 33kw Worcester. The Ideal Logic comes with a 7 year guarantee compared with an "up to" five years with the Worcester, is 35kw, and cheaper.

    The engineer has bene putting the Ideal Logic Plus in for several years and has one himself, so is fairly confident with them. 

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  • exocetexocet Frets: 1948
    Persoanlly I wouldn’t deviate from Worcester or Vaillant but if your chosen supplier is more familiar with Ideal boilers it maybe an uphill battle to move away from that.
    Ideal were really solid boilers in the 60s, 70s when basic technology was the order of the day. In my view they struggled in the same way as Potterton did to move with the times (Modulation  and reliable Condensing Boilers).

    Depending on how many people live in your house / use HW regularly (showers and baths) you might find that the Ideal boiler listed is not powerful enough for HW, look at the flow rate at 35 Degree temp difference - 14 litres per minute. Fine in summer but in Winter, the incoming mains is often less than 10 degrees so the flow rate has to reduce to meet the required output temp.

    For a 5 bed house I’d say that you’re looking at something like the Worcester Greenstar 38CDi Classic which delivers HW at 14 Litres / Min with a 40 Degree temp difference.
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  • quarkyquarky Frets: 2777
    Thanks @exocet that looks great. A neighbour had a Worcester put in last year, so I will talk to him too!
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  • strtdvstrtdv Frets: 2356
    The only reason to change IMO is if you're changing from oil to gas. 
    If you've an efficient boiler then a good sized hot water tank works very well and doesn't cost a fortune to run. I'd put in a solar hot water system before I changed to a combi (that way you have hot water through the winter when the heat is on anyway, and in the summer without using the immersion).
    Robot Lords of Tokyo, SMILE TASTE KITTENS!
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  • quarkyquarky Frets: 2777
    edited January 2018
    I don't really have any room on the south facing roof for solar though, so it would have to go on the north facing side, which is going to be pretty rubbish.. My existing boiler is almost 18 years old, and the cylinder is leaking. So the cylinder definitely needs to go, and really, the boiler should be replaced anyway (although it does still work). So a combi is cheaper than replacing the existing boiler and cylinder, and should be much cheaper to run. Or that is how it sounds!
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  • exocetexocet Frets: 1948
    The only other thing to consider is the state of the rest of your system....by this I mean radiators, valves and pipes! Your current system will be “open vent” which means that you’ll have a header tank in the loft and the system is not pressurised. As soon as you move to a combi, the system will be pressurised (more than 1 Bar). This can expose leaking valves / Pipe joints. The other thing is that modern boilers have smaller bore tubes within the heat exchanger compared to older cast iron types, unless you flush the current system through really well, you can end with issues in the new system (blockages in the heat exchanger). The plumber will flush through your current system - most likely with a power flusher / descaling agent - but this can exarcesbate the issue of old leaky valves. 

    Its not not something that you want to think about paying for at this time of year but at least consider replacing your current system completely. If you do this, you can replace your current rads with larger / more powerful radiators. The reason for doing this is that condensing boilers only run in condensing mode when the flow temperature from the boiler is at 56 degrees (approx)  or lower and with the system setup for return temperatures 20 degrees lower. Older systems in the UK were often designed with flow temperatures of 80 degrees and a return of 70. The impact is that to get best system efficiency with old rads....your house will invariably be not warm enough....or your boiler won’t be running in condensing mode. 
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  • ToneControlToneControl Frets: 11789
    exocet said:
    The only other thing to consider is the state of the rest of your system....by this I mean radiators, valves and pipes! Your current system will be “open vent” which means that you’ll have a header tank in the loft and the system is not pressurised. As soon as you move to a combi, the system will be pressurised (more than 1 Bar). This can expose leaking valves / Pipe joints. The other thing is that modern boilers have smaller bore tubes within the heat exchanger compared to older cast iron types, unless you flush the current system through really well, you can end with issues in the new system (blockages in the heat exchanger). The plumber will flush through your current system - most likely with a power flusher / descaling agent - but this can exarcesbate the issue of old leaky valves. 

    Its not not something that you want to think about paying for at this time of year but at least consider replacing your current system completely. If you do this, you can replace your current rads with larger / more powerful radiators. The reason for doing this is that condensing boilers only run in condensing mode when the flow temperature from the boiler is at 56 degrees (approx)  or lower and with the system setup for return temperatures 20 degrees lower. Older systems in the UK were often designed with flow temperatures of 80 degrees and a return of 70. The impact is that to get best system efficiency with old rads....your house will invariably be not warm enough....or your boiler won’t be running in condensing mode. 
    ah, so with old rads, the boiler would keep heating until the thermostat trips, thus not working in condensing mode??
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  • exocetexocet Frets: 1948
    exocet said:
    The only other thing to consider is the state of the rest of your system....by this I mean radiators, valves and pipes! Your current system will be “open vent” which means that you’ll have a header tank in the loft and the system is not pressurised. As soon as you move to a combi, the system will be pressurised (more than 1 Bar). This can expose leaking valves / Pipe joints. The other thing is that modern boilers have smaller bore tubes within the heat exchanger compared to older cast iron types, unless you flush the current system through really well, you can end with issues in the new system (blockages in the heat exchanger). The plumber will flush through your current system - most likely with a power flusher / descaling agent - but this can exarcesbate the issue of old leaky valves. 

    Its not not something that you want to think about paying for at this time of year but at least consider replacing your current system completely. If you do this, you can replace your current rads with larger / more powerful radiators. The reason for doing this is that condensing boilers only run in condensing mode when the flow temperature from the boiler is at 56 degrees (approx)  or lower and with the system setup for return temperatures 20 degrees lower. Older systems in the UK were often designed with flow temperatures of 80 degrees and a return of 70. The impact is that to get best system efficiency with old rads....your house will invariably be not warm enough....or your boiler won’t be running in condensing mode. 
    ah, so with old rads, the boiler would keep heating until the thermostat trips, thus not working in condensing mode??
    That's basically it. Old rads specified for 82/71 degree operating to "emit" a certain heat output won't deliver the same heat output whilst running at lower flow / return temps. So if you set your flow / return temps to run in condensing mode, your room temperature is not likely to reach your desired temp (especially in winter)! If you set the flow temp to be higher to get your desired room temperature, the boiler will only work in condensing mode whilst the return temp is lower than 56 degrees (or there abouts). It will do this during a cold start / cold house but once things heat up, the boiler will drop out of condensing mode and your lose the additional system efficiency. 
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  • quarkyquarky Frets: 2777
    edited January 2018
    So how old is old for radiators? The house was built in 2000, so are they likely to be designed for 82/71 heat? 

    From a personal point of view, I tend to have my heating set for 20 degrees. Is that likely to help the boiler operate in condensing mode? Can I typically enable/disable condensing mode, or is this something that should be automatic?
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