Why are some Advance buffers mild steel and others stainless steel?

The three types side by side

Why the small buffers are mild steel

Advance Appliances gives two reasons in its own FAQ. The 20 litre and 100 litre are its best sellers, and mild steel keeps their price competitive. The 100 litre is also box shaped, with thicker walls than the stainless buffers, so it can carry a cylinder of up to 300 litres on top.

What the stainless buffers add

The ECO stainless steel buffers are made in the UK from duplex stainless steel and guaranteed for 25 years. They are approved by WRAS, the Water Regulations Advisory Scheme, and fully recyclable, and the 150 to 300 litre models are A rated for heat loss. The installation guide rates them to 3 bar and 95°C. They cover the larger volumes, from 150 to 500 litres.

Why inhibitor matters more with mild steel

The installation guide says that because the 20 and 100 litre buffers are mild steel, the advice on inhibitor levels is particularly important. Advance's FAQ says they have a long life if the system is inhibited.

• Dose inhibitor for the whole heating circuit plus the buffer.
• Check the inhibitor level from time to time, along with the expansion vessel pressure.

Advance's terms also exclude systems where primary water is not inhibited to the correct dose, so this protects the guarantee as well as the buffer.

Registering the guarantee

Register any Advance buffer on the warranty registration page within six months of purchase; the form lists stainless buffers at 25 years and mild steel at 2. Have the serial number and commissioning paperwork ready for any claim.

For the cylinder-on-top set-up, read standing a cylinder on the 100 litre buffer.