The tank is a different question from the boiler

The most straightforward case and the easiest to inspect, because you can see all of it. Indoor tanks generally corrode from the inside out, driven by water that collects in the bottom — so a tank that looks perfect from the outside is not automatically fine.

• Look underneath and at the legs. Weeping, staining or a damp patch on the floor is the thing to act on.
• Look at the bottom seam, which is where internal corrosion shows first.
• Check the feed line from the tank valve to the burner, and whether there is a filter and a shut-off you can actually reach.
• Ask for the water to be checked. Water in the bottom of a tank is the main driver of the corrosion that ends it, and it is measurable.
• A leak indoors is a mess and an expense. It is not the environmental and legal problem that a buried leak is.

Everything that applies indoors applies here, plus weather. Outdoor tanks take rain, sun and frost, and the base they stand on matters as much as the tank does.

• Check what it is standing on. A pad that has sunk, cracked or tipped puts the tank out of level and strains the outlet.
• Look at the fill and vent lines where they enter the tank and where they run to the house. Vent whistles are worth keeping clear — the delivery driver relies on them.
• Watch for pooling around the base. Standing water accelerates external corrosion at exactly the point you cannot see.
• The gauge and the feed line want checking every year along with the burner.
• Cold-weather gelling is a supply question rather than a tank one, but an outdoor tank makes it more likely and your supplier can advise.

A different category of question. A buried tank cannot be inspected by looking at it, and a leak is an environmental and financial matter before it is ever a heating one.

• You cannot judge it by how the heating behaves. A tank can leak for a long time while the system runs perfectly.
• Establishing its condition is specialist work — tank testing, and where required removal or closure, is done by contractors who do only that. It is not an HVAC job and we will not pretend it is.
• Speak to your insurer before you need to. Cover for buried tanks varies a great deal and people frequently find out at the worst moment.
• It surfaces at sale. A great many buried tanks become somebody’s problem during a property transaction rather than during a winter.
• What we can do is service the appliance, look at the line from the tank to the burner, and tell you plainly what we can see and what we cannot.

Very common, particularly in a house you did not have the tank installed in. It is worth establishing, because the three cases are genuinely different problems.

• Follow the fill and vent pipes. Two pipes coming out of an exterior wall near ground level, with a cap and a small vent whistle, usually mean a buried tank — or a tank on the other side of that wall.
• Look in the basement for a tank on legs, and follow the feed line from the burner backwards.
• Check your deed, survey or oil delivery records. Suppliers often know, because they have been filling it.
• Ask the previous owner or the estate agent’s file if the house changed hands recently.
• We will look for it on any visit and tell you what we find. It costs nothing to ask.