Plastic we think, but it's pained to match. They have gas, on the same side of the building but the other end of the house.
That's what we thought was happening. They've been out for a while. Thankfully it's cold, but only a light frost. So I hope it's boiling over rather than the pipes bursting inside.
Husband knows someone who was called to a fire, the house had been sold to a local property seller. They didn't drain the pipes or shut off the water, but they switched off the heating. Big freeze, plastic pipes burst or displaced and didn't come together properly. So the water tank upstairs was perpetually filling and draining. By the time the neighbours heard the alarm the inside of the house had collapsed.