Worcester Boiler Safety Valve Replacement Part

This worcester bosch safety valve protects your boiler by releasing water safely if system pressure rises too high. A worn or sticking valve can cause constant dripping from the discharge pipe, pressure drops after cooling, or repeated topping up. Replacing the correct 87186439890 safety valve helps restore stable pressure control, reduces leaks, and lowers the risk of pressure-related lockouts. Always match the part number and your boiler model before ordering.

Compatibility :

• Compact: 533, 533 ErP, 535, 535 ErP
• GR4700iW (System): 12s, 15s, 18s, 21s, 24s (NG/LPG)
• GR4700iW (Combi): 25c, 30c (NG/LPG)
• Greenstar CDI Compact: 28, 32, 36 (NG/LPG)
• Greenstar CDI Compact ErP: 28, 32, 36 (NG/LPG)
• Greenstar i System Compact: 27, 30 (NG/LPG)
• Greenstar i System Compact ErP: 27, 30 (NG/LPG)
• Danesmoor System: 12/18, 18/25, 25/32 (incl. ErP/ErP+)
• Danesmoor System External: 12/18, 18/25, 25/32 (incl. ErP/ErP+)
• Danesmoor System Utility: 12/18, 18/25, 25/32 (incl. ErP/ErP+)
• Heatslave II: 12/18, 18/25, 25/32 (standard / ErP / ErP+ / 2022)
• Heatslave II External: 12/18, 18/25, 25/32 (standard / ErP / ErP+ / 2022)
• Heatslave II Ext: 12/18, 18/25, 25/32 (ErP)
• Greenstar SI Compact: 25 (NG/LPG), 30 (NG/LPG)
• Greenstar SI Compact ErP: 25 (NG/LPG), 30 (NG/LPG)

Important fitting advice

We recommend that all parts are fitted by a fully qualified Gas Safe registered engineer. If you need help confirming the right part, contact us our team has 10+ years of boiler spares knowledge and friendly chat support to help you quickly.

Delivery

At Boiler Spares Hub, we dispatch orders within 1 working day (Monday-Friday). Orders placed outside working days will be dispatched on the next working day. For delivery options available for this product, please add it to your basket or check our delivery options page.

Returns

We accept 30-day returns. Returns must be in an unopened, sealed box. If we find the item has been used or installation was attempted, we may refuse the return.

Frequently Asked Questions (FAQs)

1. What does a boiler safety valve do?
It releases water safely if system pressure gets too high, protecting the boiler and pipework.

2. What are common signs it needs replacing?
Dripping/constant discharge outside, pressure dropping after cooling, frequent topping up, or random pressure spikes.

3. Is dripping always the safety valve fault?
Not always over-pressurisation from a failed expansion vessel can make the valve open. But once a valve has lifted, it can start leaking.

4. How do I confirm this fits my boiler?
Match part number 87186439890 and confirm your boiler model / GC number from the data badge.

5. Do I need an engineer to fit it?
It’s part of the sealed heating circuit and usually needs draining/refilling and pressure checks best done by a qualified heating engineer.