OEM vs compatible boiler parts — what is the difference?

Last updated 9 October 2026

When your boiler breaks down, you need a part. But which grade? OEM genuine, compatible alternative, refurbished, or obsolete-sourced? Here is a clear, honest comparison so you can pick the right part for the job.

The four grades at a glance

OEM genuine

The original manufacturer's part. Made by the same company that built your boiler, to the same specification. Identical in every way to the part that came out.

✓Exact manufacturer specification
✓Full manufacturer warranty
✓Guaranteed fitment

Compatible alternative

A third-party part made to match the OEM specification. Tested for fitment and performance. In many cases the internal components are made in the same factories.

✓Matched to OEM specification
✓Hanicks fitment guarantee
✓Typically 20–40% less than OEM

Refurbished

An original part that has been removed, cleaned, tested, and restored to working condition. Common for PCBs and gas valves where the OEM part is expensive.

✓Original manufacturer part
✓Tested and certified working
✓60–70% less than new OEM

Obsolete-sourced

No longer manufactured. Sourced from specialist stock networks — new-old-stock, decommissioned units, or salvage. When the big nationals have stopped listing it, we try to find it.

✓No longer in production
✓New-old-stock or tested salvage
✓The only route for discontinued boilers

Full comparison

Factor	OEM genuine	Compatible	Refurbished	Obsolete
Price	Highest	20–40% less	60–70% less	Varies
Manufacturer warranty	Full manufacturer warranty	12 months (supplier)	6–12 months (supplier)	No warranty — sold as-is
Hanicks fitment check	Verified	Verified	Verified	Best-effort — may need confirmation
Identical to removed part	Yes — same part	Matched on specification	Same part, restored	Yes — original part
Typical availability	In stock, same-day dispatch	In stock, same-day dispatch	Check stock — limited quantities	Sourced to order – 2–5 days
Best for	Under warranty, critical systems, peace of mind	Out-of-warranty repairs, cost-sensitive jobs	Expensive PCBs and gas valves	Discontinued boilers, keeping old systems running
Gas Safe consideration	All grades must be fitted by a Gas Safe registered engineer for gas appliances. The grade of part does not change the legal requirement for who does the work.

Which grade should I choose?

If the boiler is under manufacturer warranty: always OEM genuine. Using a non-OEM part will void the remaining warranty.

If the boiler is out of warranty and you want reliability: OEM genuine is still the safest choice, but a compatible alternative from a reputable supplier is a practical compromise. Hanicks verifies fitment on every compatible part before dispatch.

If the part is expensive (PCB, gas valve): consider refurbished. A tested, certified PCB at 60% less than new is often the right call on a boiler that is otherwise running well.

If the boiler is discontinued: obsolete-sourced is your only option. Hanicks invests in sourcing networks specifically for these cases — the parts the big nationals have stopped listing.

Frequently asked questions

If your boiler is still under the manufacturer's warranty, using any non-OEM part will generally void the remaining warranty. Check your warranty terms — most require original manufacturer parts for the duration of the cover. Once out of warranty, compatible parts have no bearing on warranty status (because there is none).

It depends on the part. For simple mechanical components — seal kits, electrodes, sensors — compatible parts are often made to the same specification and perform identically. For complex electronics (PCBs) and gas-critical components (gas valves), OEM is the safer choice. Hanicks only stocks compatible parts that have been verified for fitment and tested against the OEM specification.

Before any part leaves our warehouse, a member of our technical team checks it against the appliance make, model, and GC number. If there is any doubt about compatibility, we contact you before dispatch. This is not an automated check — it is a human who knows the product range. It is the reason engineers come back to us: they do not make a second trip.

Yes. If a part does not fit the appliance you specified, we will arrange a return and refund or exchange. Because we verify fitment before dispatch, this is rare — but it can happen with older or non-standard installations. Contact us on 01302 279234.

Most Worcester Bosch, Baxi, and Vaillant boilers come with 5–10 year warranties when installed by a registered installer. Check your installation paperwork or the manufacturer’s warranty portal. If you are unsure, call us on 01302 279234 and we can look up the standard warranty period for your model — though we cannot confirm your specific installation without the original installer’s details.

Need help choosing?

Not sure which grade fits?

Search by part number, product name or brand. Our technical team confirms fitment before you pay.

Call the technical team 01302 279234