Underfloor heating fused spur

Discussion in 'Electricians' Talk' started by Kadir7103, Nov 28, 2022.

  1. Kadir7103

    Kadir7103 New Member

    Hello, I have UFH in my kitchen which is connected to a 13amp fused spur. Last night I noticed a smell coming from the fused spur and noticed that the fused area had melted away. My question is can I replace the 13amp fuse for a 20amp fuse?
  2. dai.versity

    dai.versity Active Member

    No, 13Amp is the biggest size, have you checked for loose connections? do you know the kw load of the u/f heating?
  3. adgjl

    adgjl Screwfix Select

    No. The maximum fuse size in the BS1363 size is 13A.

    Unless it is a huge kitchen, a 3kW UFH system should get uncomfortably hot quite quickly.
  4. Notnowvicar

    Notnowvicar Active Member

    Sorry the fused area had melted....holyfuksometingwong...get it checked.
  5. Kadir7103

    Kadir7103 New Member

    Thank you for the reply guys. Unfortunately I do not know the UFH matt size. I have checked for loose connections and all seems tight. What is my options? Should I replace the fused spur for a 20amp double pole?

    Attached Files:

  6. The Happy Builder

    The Happy Builder Screwfix Select

    Unless it is a dedicated circuit just for the UFH you should not replace the SFCU with a 20 amp switch.

    What is the area of the floor with UFH supplied from this SFCU?
  7. Tony Goddard

    Tony Goddard Screwfix Select

    As happy says above

    plus, occasionally such fittings do melt / overheat purely due to loose connections within. I would replace the fused spur, use a quality brand such as Schneider, Hager, MK, Crabtree etc...

    When you take the spur off you may find the UFH mat's rating label is still wrapped round the tail of the mat.
  8. Kadir7103

    Kadir7103 New Member

    I have replaced the spur and switched on the underfloor heating. After about 15 mins off running the switch spur starts to heat up. Its at this point i switch it off in fear it will either blow up or burn my house down. Lol

    Just spoken to the tiler and he stated that the extension area has two UFH matts. one matt is 16m2 and one is 6m2 both running into one thermostat.

    Abit of back ground on the wiring in my house. From the consumer unit off a 20a mcb to the 13amp switch spur, then to thermostat.
  9. The Happy Builder

    The Happy Builder Screwfix Select

    Taking Warmup UFH as an example:
    StickyMat comes in two different power variants; 150W/m2 and 200W/m2, so it is ideal for use as a primary heat source and in rooms with high heat-loss such as conservatories.

    Assume 200 watts per square metre

    (16+6) x 0.200 kW = 4.4 kilowatts = 19.2 amps.

    Assume 150 watts per square metre

    (16+6) x 0.150 kW = 3.3 kilowatts = 14.4 amps

    The SFCU is under rated and it will melt, as will any replacement SFCUs.

    However the thermostat itself is probably rated at 16 amps, so if they are higher rated UFH mats that might melt as well.

    Ideally each mat should be probably be on separate thermostats, but presumably that’s not practical now as it means taking the floor up to fit another sensor.

    If it’s a dedicated 2.5 mm circuit with a 20 amp circuit breaker it could be possible to replace the SFCU with a 20 amp Double Pole switch, but it may need the thermostat to be connected to supply the UFH through a relay to protect the thermostat.

    You need to get an electrician to accurately measure the current draw when the UFH is turned on when the floor is cold to determine what remedial work is required.
    Kadir7103 likes this.
  10. Kadir7103

    Kadir7103 New Member

    Thank you so much, I will call out an electrician and get it checked properly

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