Is this something I can change myself or should I call an engineer?
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Discuss Vaillant boiler always exceeds set temperature in the Boilers area at Plumbers Forums
Thanks. Finally, this is a system boiler so it powers 7.5 radiators but also a 150L unvented cylinder when the hot water is on. It’s the same circuit ie we don’t use the hot water function of the boiler. Does that change the equation?
There can be two reasons for this, one is that the boilers minimum output is greater than the heat demand from the rads, in which case the burner will cut out when the flow temperature exceeds the boiler setpoint temp by 5C. The other reason is if the burnercuts out within a minute or two of firing up if the boiler hasn't modulated down fast enough. You can try I creasing the boilerflow temperature to 75C or more and yes you can kw from 16kw to say 8kw, might help
Thanks! I’ve noticed something different. The issue only seems to happen when the Nest has the hot water on. The hot water goes to an unvented cylinder.
When the radiators are on, the 64C is maintained. When they are off but the unvented cylinder is heating, the boiler turns on, goes straight to 70C, cuts off, then repeats over and over again. is the unvented Cylinder broken? I thought if the water was on but it was at temperature, it would trigger the boiler to go on.
When the radiators are on, the 64C is maintained. When they are off but the unvented cylinder is heating, the boiler turns on, goes straight to 70C, cuts off, then repeats over and over again. is the unvented Cylinder broken? I thought if the water was on but it was at temperature, it would trigger the boiler to go on.
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Reduce the boiler output to 6 or the lowest you can do
The attacher is on the cylinder… it’s set to 65C (I think it always has) and this is higher than the boiler flow temperature. This should be dialed down 5-10C?
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Boiler should be 65 cylinder stat wants reducing to 60
Still happening with the boiler set to 64 and the cylinder to 50.
What is the expected behaviour? Is the boiler supposed to turn off when the cylinder signals it’s at temperature (but the Nest indicates it’s still on, waiting to signal
To the boiler that it needs to heat its water?)
Should I call an unvented cylinder engineer or should I try reducing the boiler to 8KW?
What is the expected behaviour? Is the boiler supposed to turn off when the cylinder signals it’s at temperature (but the Nest indicates it’s still on, waiting to signal
To the boiler that it needs to heat its water?)
Should I call an unvented cylinder engineer or should I try reducing the boiler to 8KW?
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Nest will still signal it needs heat as they don’t talk to each other the stat controls the temp
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Once the nest is set for water on eg calling the cylinder stat takes over and controls the temp
Suggest running off say 10 to 15 litres of HW with tap opened for 5 minutes or so, then programme the CH + the HW to come on together then switch off the CH only after 3 or 4 minutes and see if the boiler continues to fire until the cylinder is fully heated.
Thanks for all your help everyone. The house is thankfully warm and we still have hot water so I can’t complain at the moment, even if it doesn’t seem to be operating as it should.
I dropped the power to 8kW to see how things runs.
I assume it’s safe to play with the power output?
I dropped the power to 8kW to see how things runs.
I assume it’s safe to play with the power output?
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Yes as it’s just settings will soon tell you no if it doesn’t like one
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Attaching photo of the UFH located under my stairs, i cant rem for 100% the loop lengths of the pipe run. Kitchen is split in into 2 circuits i know one was about 70m and the other was about 30-40m. Same with the living room they were about 75m each.
I have been playing around with the Flow rates recently but at present they are set to around 3l and pump speed to 3. I have recently tried to have the rates at around 2l with the pump speed on 2 but the kitchen seem to take a very long time to warm up due to higher heat loss because i have very large 3 panel bifold doors.
Let me know if u need any other info...ill try my best to get this..
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Would doing this have any negative impact on the boiler?
Attaching the photo of the table for anticycle times, so at 60c as set currently would it be?
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Works out to around 6 kw on the ufh maybe
You want a difference of 7 degrees between flow and return on each circuit when warm so alter the flow meters to achieve this if you can
You want a difference of 7 degrees between flow and return on each circuit when warm so alter the flow meters to achieve this if you can
No, it shouldn't, 60C+20C(time) = anticycle time of 6 minutes, 60C+25C=7.5minutes & 60C+30C=9minutes.
I would increase that (d.002) initially to 25, a 7.5 min anticycle time, as it might reduce the starting temperature low enough to get the boiler away without exceeding the target temperature.
I would increase that (d.002) initially to 25, a 7.5 min anticycle time, as it might reduce the starting temperature low enough to get the boiler away without exceeding the target temperature.
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yes thats what i have been trying recently to get, i dont know what my return temp are to be honest is there a way to check this?
when i checked the diagnostic menu on the boiler d.41 (i think it was) it was showing me like 55c, im not entirely sure if this is the return from the manifold or the whole system? as it seemed very high because when i touch the return copper pipe (one on the left in the pic i uploaded) its not very warm even when the UFH has been on for few hours. it could be due to the way the pipes are laid (single serpentine).
I dont have a temp gauge on the return part of the manifold, im certain the difference is higher than 7c because the UFH pipe layout is Single serpentine (this was a total mess by the plumber who did it and i didnt know anything about ufh at the time to correct anything). however i cant change this now so im just trying to find a way to get this best as i can. I will increase the flow rates and see if this changes.
What are your thoughts on the suggestion by John.g to change the boiler to 6kw and increase the Anticycle time. Im thinking to give this a try tomorrow morning and see how the system behaves...
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Thanks John.g - i will give this a try tomorrow morning and report back.
I know a buffer tank is an option but i just dont have space near the boiler to fit this as this would solve the anticycle issue and allow the boiler to run in fully condensing mode.
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