

The Webasto Thermo Pro 90 is a powerful, robust and highly efficient 9kW water heater engineered for heavy commercial vehicles, minibuses, motorhomes, RVs and marine systems.
This model – 9034839A – is the High Altitude Special Edition, designed to deliver reliable performance in demanding environments and elevated regions where standard heaters struggle.
With advanced technology such as automatic altitude adjustment, Arctic Start and intelligent heat modulation, the Thermo Pro 90 ensures consistent heating even in severe weather and high-elevation conditions.
This 9034839A High Altitude version includes enhanced altitude compensation, allowing the heater to operate correctly where oxygen levels are reduced:
Automatic altitude adjustment up to approx. 4,500 metres (14,760 ft) above sea level
Improved combustion stability at high elevations
Ideal for mountain routes, alpine environments, and high-altitude vehicle conversions
Reliable cold-start performance thanks to Arctic Start technology
Up to 9.1 kW of heating power – fast warm-up and powerful heat output
Engine-independent heating for year-round comfort
Arctic Start ensures quick heat delivery even in sub-zero conditions
Low power consumption thanks to highly efficient design
Quiet operation for comfort during night use
Long service life backed by premium Webasto engineering
Suitable for new installations or retrofits
Supplied as a genuine Webasto unit with 36-month warranty
A complete installation package:
Webasto Thermo Pro 90 (9kW) High Altitude Heater – 9034839A
Integrated 24V Water Pump
Your selected controller (choose above)
Water connector pipe for engine pre-heat
Stainless-steel exhaust with silencer & fixings
Complete wiring harness and all connectors
Combustion air intake pipe
Exhaust silencer
Fuel dosing pump
Additional water pump
Fuel supply pipe & plastic fittings
Mounting bracket
Everything required for a clean, professional installation.
Perfect for high-demand or high-altitude environments:
Small vans & minibuses
VW T5, caravans & mobile homes
Campervans & RV conversions
Horseboxes
4×4 vehicles and off-grid builds
Replacement heater upgrades
Mountain or high-elevation vehicles
If you need a tailored system, we can supply bespoke kits built to order.
Contact our sales team with your requirements.
Select your preferred controller from the drop-down options above to complete your installation setup.
Warranty Terms
Mellor Solutions Ltd trading as Mellor Online is an authorised distributor of heating parts and heater kits for the vehicle and marine markets.
Warranty Coverage:
Additional Services:
Returning a Heater:
Customer Responsibilities:
Exclusions and Important Notes:
Returns Policy
Our returns policy applies to consumer purchases only (not business or trade orders).
Our returns policy does not cover items that fall under manufacturer warranties. If you believe your item is eligible for warranty service or you wish to return an item for a refund, please contact our support team or email us at sales@melloronline.co.uk.
Refunds and Cancellation Rights
You have the right to cancel your order within a 14-day cooling-off period, starting the day after you receive your items. Refund requests can be submitted within 30 days of the invoice date. Refunds will be processed within 14 days of receiving the returned goods.
Notification of Intent to Cancel
To cancel an order or request a refund under the UK Consumer Contracts Regulations 2013, you must inform Mellor Solutions Ltd trading as Mellor Online of your intention by phone, email, WhatsApp, or post within the applicable period. This is 14 days for cancellations and 30 days for refunds.
Upon receiving your request, we will send you a confirmation and authorization to return the goods. Please include your original invoice number with your return. All items must be in a resaleable condition
Upon receiving your request, we will send you a confirmation and authorization to return the goods. Please include your original invoice number with your return. All items must be in a resaleable condition.
Return Shipping
You are responsible for returning goods using an insured and trackable shipping method at your expense. We will only consider refund requests if there is proof of delivery to Mellor Solutions Ltd trading as Mellor Online from your chosen courier. Once we receive the goods, we will issue a full refund minus any delivery charges.
If you cannot arrange a return, please contact us. We can arrange collection for you, but a fee will apply, which will be deducted from your refund.
Please note that delivery charges from the original purchase are non-refundable, as the service is completed once the order is placed.
Processed and Dispatched Orders
Orders that have already been processed or dispatched cannot be canceled; however, they can be returned for a refund once received by the customer.
We strive to facilitate a prompt refund process upon receiving returned items.
Return Address
FAO: RETURNS
Mellor Online
139 Manor Road
Ossett
West Yorkshire
WF5 0LQ
United Kingdom
Specific Terms
Your Statutory Rights
Your statutory rights are unaffected by the above terms. Consumers, excluding business trade customers, are further protected under the UK Consumer Contracts Regulations 2013.
For any questions, please contact our support department before returning any items.
Shipping Information: UK & Worldwide
UK Delivery:
International Delivery:
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