Ho, I'm looking to replace my valiant ecotec plus 831 boiler which I believe is 25.5kw. I live in a detached bungalow with 8 large double radiators, a single bathroom with boiler fed shower and bath. Bath currently takes a good 20/25 mins to fill. Pipe runs are quite long and the hot taps can take around 45 secs to get warm. My installer has quoted for a 30kw baxi 800 combi 2 to replace which I'm happy with but is this oversizing and may end up costing me more money to run?
Boiler kw advice
- Thread starter mole81
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A bigger boiler isn't going to solve a longer pipe run/the need to dump X litres of cold water down the sink before it comes hot
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If long heating time is the issue have you considered moving the boiler closer to the most frequently used taps? I wouldn't factor a bath into the equation, but prioritise kitchen sink then main shower
The boiler will hardly be undersized for radiators you have
831 may be dated but hardly ready for the grave
Talking from experience as have the same boiler
You don’t need a new boiler but an engineer who will look at the system and give you honest opinion. For this you need a service/ repairer who is not just nailing boilers onto the wall
Measure radiator sizes, look up the heat output- I would be surprised if your boiler is not up to it.
Feel the flow and return pipes after the system has been running for an hour or so. One pipe should be hot to grasp and other be able to grasp but still hot. If the second pipe is cooler then may well be circulation issues.
831 may be dated but hardly ready for the grave
Talking from experience as have the same boiler
You don’t need a new boiler but an engineer who will look at the system and give you honest opinion. For this you need a service/ repairer who is not just nailing boilers onto the wall
Measure radiator sizes, look up the heat output- I would be surprised if your boiler is not up to it.
Feel the flow and return pipes after the system has been running for an hour or so. One pipe should be hot to grasp and other be able to grasp but still hot. If the second pipe is cooler then may well be circulation issues.
Are you sure that the boiler is firing continuously from a cold start and isn't cycling?.
Have a look, or get someone to look at the diagnostic, "d", codes.
Ensure that d.0, Heating Part Load, is set to the max output of the boiler, 25kw?.
Keep checking the boiler flow & return temps, d.40&d.41 while the boiler is heating up and also check them when the boiler is up to temperature and starts modulating down and again maybe 30 minutes later.
Have a look, or get someone to look at the diagnostic, "d", codes.
Ensure that d.0, Heating Part Load, is set to the max output of the boiler, 25kw?.
Keep checking the boiler flow & return temps, d.40&d.41 while the boiler is heating up and also check them when the boiler is up to temperature and starts modulating down and again maybe 30 minutes later.
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Yes correct for the age. Definitely consider a new boiler as last time I price checked a main heat exchanger for that range was £699 and that’s just the part.
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I found with a bath, it needs so much water, the cold water before the boiler heats up is not a problem, it just means you add less cold latter. As to filling time, you may watch and wait for 5 minutes, but as it gets to 20 minutes, one sets a reminder, so be it 15 or 30 minutes is really not difference, you run bath before it is wanted, as set a timer to remind one.
So it is really only the sink taps that matter, and likely the smaller the boiler and pipes, the quicker hot water arrives at the taps, at work we call it the price of a match, we have far bigger boilers, which actually boil water, on a heritage railway, but the problem is the same, cost to turn on the boiler, before you get any hot water,
In my case, I had an iboost+ fitted to my immersion heater, which logged how much electric used, typical week around 3 kWh, my boiler is 20 kW, it does not modulate, and I would run it three times a week, around 20 minutes a time, around 25 kWh, clearly for me electric is cheaper. It will depend on the house, but I feel when we have the kitchen done, an under sink 5 litre electric water heater will both save money and reduce the wait for hot water.
As said my boiler is simple on/off, so my TRV head reports a massive hysteresis, the minium output is important, if your boiler can modulate enough, you will get a smooth line, but if it needs to cycle then a hysteresis, and most of the time one only needs a small amount of heat to maintain the temperature, so the lower it can go the better.
I personally would not go down the combi route, unless you need the room.
So it is really only the sink taps that matter, and likely the smaller the boiler and pipes, the quicker hot water arrives at the taps, at work we call it the price of a match, we have far bigger boilers, which actually boil water, on a heritage railway, but the problem is the same, cost to turn on the boiler, before you get any hot water,
Very good advice, also idea of a local heating device for remote taps, I used the boiler for DHW, I had been told in my case, oil is cheaper than electric, well it is, but what we are looking at is the waste. It to get 1 litre of hot water, you run off 4 litres first, then you have wasted 4 litres of heat, which will be left in the pipes cooling, and also heating your home, winter not a problem want home warm, summer you may need to run an AC so you are not only paying to heat the water but also paying to cool it as well.
In my case, I had an iboost+ fitted to my immersion heater, which logged how much electric used, typical week around 3 kWh, my boiler is 20 kW, it does not modulate, and I would run it three times a week, around 20 minutes a time, around 25 kWh, clearly for me electric is cheaper. It will depend on the house, but I feel when we have the kitchen done, an under sink 5 litre electric water heater will both save money and reduce the wait for hot water.
As said my boiler is simple on/off, so my TRV head reports a massive hysteresis, the minium output is important, if your boiler can modulate enough, you will get a smooth line, but if it needs to cycle then a hysteresis, and most of the time one only needs a small amount of heat to maintain the temperature, so the lower it can go the better.
I personally would not go down the combi route, unless you need the room.
How old is your house?
Fill a bucket at the cold tap of your kitchen sink (and the garden tap if you have one).
Time it to full.
How many litres per minute does it deliver?
Then try the hot and cold bath taps, separately.
Combi boilers are limited in the rate at which they can deliver hot water, but a full bath is usually around 100 litres, which should not take 20/25 minutes.
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