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Perfect 35 Undersink Instant Water Heater, 3.5KW

£108.98 inc VAT
£90.82 exc VAT

Perfect 35 Undersink Instant Water Heater, 3.5KW

Ideal for providing hot water to a hand wash basin

Product Code: 133362

35 reviews
£108.98 inc VAT
£90.82 exc VAT

Order now for delivery 24th January

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  • Warranty: 2 Years
  • 30 day money-back guarantee
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Product information

Power - 3.5 kW
Brand - HSD
Height - 15 cm
Width - 13.5 cm
Depth - 7.5 cm
Weight - 0.9 kg

Perfect 35 Instant Undersink Instant Water Heater - 3.5KW

The latest in water heater design and manufacturing for reliability and durability

This small instant hot water heater uses simple electronics to control water flow and temperature providing a reliable and steady flow of water to a bathroom hand wash sink. It is non vented and has a minimum pressure requirement of 10psi or 0.7 bar.

Low wattage
This low wattage water heater provides hot or warm water for wash basins (if you are looking for a similar unit for a lightly used sink or en suite conversion alongside a pre-installed electric shower, we would recommend the more powerful Perfect 55 water heater that produces hotter water for the same flow rate and hotter water in general).

Designed with space saving in mind
The unit (with its small size) fits under sinks and takes up less space than traditional tank water heaters. If the sink or basin you are using is a distance from your central heating hot water source, we highly recommend using a Perfect water heater. This avoids the need for litres of water to run wastefully whilst you wait for hot water.

Highly efficient

Instant water heaters do not need to needlessly heat up 10-15L of water for only 5L to be used. This unit only heats up the water as it runs through the unit, saving you energy and water compared to traditional undersink water heaters.

Extremely versatile
Compatible with any tap from ordinary through to single or monobloc taps (peak performance is found with a spray tap fitting)
Easy installation with flexible hoses and rubber gaskets for simple connection by a qualified plumber (not supplied)

  • Not suitable for use with a shower or bath
  • Cold water inlet temperature during winter based on 15C
  • Cold water inlet temperature during summer based on 20C
  • 15.2 amps fuse needed


Rating 4.5 out of 5 based on 35 reviews.
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Showing 1 to 10 of 35 Reviews
KMW Ipswich
It provides a small stream of luke-warm water adequate for hand washing but it is so small and easy to hide in an undersink cupboard that it is just about ok overall.
23 Oct 2018
Rob Slater
Good product, works well, but perhaps I should have ordered a higher wattage version for the water to run quicker.
13 Oct 2018
Does exactly what it should do
30 Aug 2018
Michael Bailey
I would have grave reservations about recommending this product as it has been fitted professionally but gives only warm water and at a very poor flow rate. It is better than the cold water I had before but I will probably replace the item next year for a higher performance version or different product entirley.
7 Mar 2018
Slow flow at maximum water temperature but perfectly adequate for hand washing at normal flow.
26 Sep 2017
Pauline Hassett
Best product, best company!
15 Sep 2017
Sceptical at first as to whether this unit would do the job. It does, and very well. Good little heater. Easy to install and sits very well in the vanity unit. Takes up minimal space. So far, so good.
14 Sep 2017
Stewart, Northamptonshire
Product very good. Fits neatly into hand basin unit.
5 Feb 2016
Edward, Lancashire
very satisfied
28 Jan 2015
Michael, Cambs
Great piece of kit. I had one in my previous house and got the local plumber to fit this one. He hadn't come across them before and was surprised how easy it as to fit and how ell it worked
20 Dec 2014

Documents & Instructions

Frequently asked questions

Does this heater need special connection to the electricity supply, or can it run on a normal plug? Also, when you say small wash basin, how small is small?
This unit does not come with a plug, it needs to be spurred in and is only for hand wash.
Hello we have previously bought vented units because installation is very simple and no specialist accessories are needed, can you tell me if this unit needs an external pipe for any water to drip from, also does this unit come with all the parts necessa
The unit doesn't need an overflow pipe just a mains feed and a pipe to the tap. Unfortunately the tap is not included however everything else is installed.
can this unit be spurred off ring main and and would you be able to provide hot water for two basins next to each other
As the unit is above 3KW it needs thicker cable than standard ring main.
Hi, need to install 3 underbasin water heatesr for handwashing, but the locactions are in the middle of a large building. We cannot install safety release pipes as required by 'storage' type heaters. Am i right in understanding that these units are 'on-
These units are fine for hand washing and require no external drain.
can this unit be fitted be upside down (with the inlet and outlet pipes facing down)?
This unit can not be fitted upside down for safety reasons as it has a flow switch that would not work if fitted up side down. 
I have 8 bar water pressure where I live can I fit this with a pressure reducing valve to bring it inline with the max of 6.5. Thanks Alan
The heaters will tolerate a water pressure of up to 10bar, so 8 will be OK.  you can install a pressure reducer but not within 1 meter of the heater to allow for any backpressure relief  from the heater. 
Is the water temperature hot enough for washing up dishes, etc? Is the maximum temperature adjustable? What output temperature is normal?
The temperature of the water is hot enough to wash up dishes however the maximum temperature can not be adjusted. Please click on the PDF attached to the product for the temperature rates as this depends on the flow rates. 
Hi Can I use Perfect 50 to supply kitchen sink and bathroom basin in a small flat. ???
You would need one water heater per sink. 
Can this heater be employed under a sink in a wet room where it will be within splash range of a shower?
This unit has an IP rating of IP24. You will have to contact your electrician to see what Zone this will be plumbed into for your personal circumstances and he will advise if this will be suitable for your needs. 
Does it come with full fitting instructions, having not fitted one before.
This unit does have full instructions however it will require a qualified tradesperson to fit the unit due to the manufacturer warranty. 
Installed a perfect 3500 water heater earlier this year but it's stopped working. Power is reaching the unit and the light comes on when you run the tap but no hot water. Have checked the flow. Is there a reset for the element ? Cheers
If you could please check the following:
- is the voltage too low (supplying installatio overloaded)
- the temperature of the entering water may be too low.
- water flow too high.

If these do not assist in this matter please contact our Customer Services team on 08000 913171
Can this unit be fed to the mains hot water feed
No this is because the heaters run on full power, raising the water temp according to flow rate based on an entry temp of circa 10-15*. If the entry temp is higher than 20* the water will be super heated and trip the thermal break inside. 
Re quick code 133362 3.5 kw instant water heater: 1) Does it need a special venting tap? (ie not an ordinary one) 2) Does it have hot maintained storage ie does it need 24/7 thermostat controlled trickle feed electric power? Many thanks. Stuart
This is an instant water heater therefore it does not have need a venting tap. This does not store any water; it heats as it goes and is connected to the mains water. For full instruction how to fit the unit please see the PDF attached to the web site.
Can the perfect 35 be connected to standard mixer taps?
The Perfect 35 can be connected to standard mixer taps.
Do the prefect 35 need an expansion vessel
The Perfect 35 Instant Water Heater does not require an expansion vessel.
Do I need a vented tap with the 35 model
The Perfect 35 does not require vented taps and can be used with ordinary non-vented taps.
Hi, is it essential that the tap be fitted with the spray Nozel fitting or can I use it without one or an aerated tap insted?
The spray nozzle is optional but fitting it into the tap will give optimal performance of the water heater.
Hi, I asked this question on Friday / Saturday, but have not had a response. I would appreciate a reply. In answer to someone else's question you said this needs to be run off a spur with a 15.2 amp fuse. I can't find a a fused spur, with a suitable fuse
We do not stock 15.2amp fused spurs and we would advise you to contact a qualified electrician to install the water heater correctly.
can you use this for a shower for dogs i.e control temperture
Although we have customers who purchase the Perfect 55 water heater (our code 133365) for hair salons, we cannot recommend this to wash your dog, since this product is not designed for that purpose. The temperature of the hot water is controlled by the flow rate of the incoming cold water and can be variable.
Will the cable from a 3kw immersion heater be sufficient to operate the heater.?
We would not recommend to use the cable from a 3kw immersion heater. The 3.5kw water heater will need the correct current with a fuse of 15.2amps. As with any electrical appliance of this nature, we would recommend to have the water heater installed by a qualified electrician/plumber.
What are the dimensions of the Perfect 35 unit ?
The dimensions are H 15 x D 7.5 x W 13.5cm.
Can these units be used with a basin TMV (Thermostatic Mixing Valve) ?
This product cannot be used with a Thermostatic Mixing Valve.
1) Does Perfect 35 Undersink Instant Water Heater require expansion vessel? 2) Is this unit suitable to fit more than one wash handbasin/s?
This water heater is an instantaneous water heater and does not need an expansion vessel. It is suitable to provide water to one hand wash basin only for optimum performance.
Does a low mains water pressure of 1.5 bar affect the working of the unit? Are spray nozzles in the tap used necessary for some reason?
This water heater can run on a minimum of 0.7 bar of water pressure, so 1.5 bar would be okay. The spray tap fitting provided ensures peak performance from the water heater.
Hi is it possible to install this in a room away from the sink ie in a cuboard approx 1.5m away from where the sink will be located?
Yes, but there may be a run off of cold water out of the length of piping. If the heater is not used for longer periods, the water in the 1.5m piping will cool, so when the hot water tap is turned on it will have to drain the cold water in the pipe.
Just purchased a "35" unit. Being installed under in cupboard under sink in small cloakroom. Can the 20 amp water heater box be fitted close to heater, i.e. In cupboard or does it have to be fitted outside? Many thanks
As long as the 20 amp fuse box is sealed and accessible, it can be installed anywhere on the circuit. However, a qualified electrician will have better advise on your particular circumstances.
Can inlet to the 35 Unit be fed from the domestic hot water system or will the pressure be too low?
This is a cold feed only water heater, working from the mains water pressure.
Do you need a expansion vessel and blow off for unit
No, this water heater does not need an expansion vessel or a blow off valve.
Can this unit be fitted with the supply & feed at the bottom?
Unfortunately, this water heater cannot be fitted with the supply and feed at the bottom. However, if you are looking for an over sink water heater, the Perfect Mix would be suitable. It comes supplied with a spout which is ideal for a hand wash basin. Please see details below:
Can this unit be fitted upside down with the feed & supply at the bottom?
This water heater cannot be fitted upside down. It must be installed the correct way up, with the water connections on top of the unit.
i am in need of hand wash water supply to fit in vanity unit but without plumbing needed. can you help
This unit does not come with a plug, it needs to be spurred in and is only for hand wash.
Please see the link below to the instructions :
Would this unit perfect 35 work in a touring caravan for hot water supply.
This would be suitable for light use hand wash not for a 15L Kitchen sink or heavy use. A 16amp RCD breaker is required. This must be fitted by a qualified tradesperson.

Please see instructions and documents below
Will this 35 heater work off a standard ring main, as the ring main is 2.5mm cable off a 20 amp fuse, regards
The 3.5kw unit is rated at 15.2amps and requires a 16amp RCD breaker - 1.5mm cable.
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