Worcester Bosch Washer M4 Large 87161098130

This is a Worcester Bosch M4 large washer, supplied under part number 87161098130. It is a small sealing component used at a threaded or bolted joint inside the appliance, where it sits between mating faces to close the gap and stop water or gas-path leakage. It belongs to the Worcester Bosch Greenstar Heatslave family of oil-fired boilers and combi units, and is also listed against the Heatslave OSO variants.

• A weep or drip at a joint after the appliance has been reassembled or serviced
• Water staining, scale trails or corrosion around a threaded connection or flange face
• The washer has hardened, flattened or cracked and no longer sits proud of the mating face
• A joint that will not seal despite correct tightening, indicating the washer has lost its compression
• Traces of water inside the casing near a pump, valve or pipe connection

• Confirm your appliance model against the compatibility list, as the same washer is used across several Heatslave variants
• Check the part number on the existing component or in the manufacturer's parts diagram before ordering
• Note the alternative number 1015571, which may appear on older documentation or stock listings
• If the joint is being opened as part of a repair, check whether any other seals or gaskets at the same connection also need replacing