What Is A Low Loss Header?

A low loss header (also called a low loss header or hydraulic separator) is a clever piece of pipework that improves the performance and longevity of modern central heating systems — especially those with multiple heating zones, heat pumps, large radiators or several boilers working together. Many UK homeowners and landlords install one when upgrading to high-efficiency condensing boilers or adding extra heating circuits.

If you’re planning a system boiler upgrade, adding zones or installing a heat pump and wondering whether a low loss header is necessary for your property, request a new boiler quote from Boilers 2 Go today — their heating design experts can assess your system and recommend the most efficient, cost-effective layout.

What Is A Low Loss Header?

A low loss header is a vertical section of large-diameter pipe (usually 65–150 mm depending on system size) fitted between the boiler primary circuit and the secondary heating circuits (radiators, underfloor heating, hot water cylinder coil) that allows water to flow at different speeds and pressures in each part of the system without interfering with each other.

How Does A Low Loss Header Work?

A low loss header works by creating a zone of very low flow velocity where the boiler can circulate water quickly and efficiently while the secondary circuits draw only the flow they actually need. 

This hydraulic separation prevents the boiler pump from “fighting” against zone valves, pumps or thermostatic radiator valves, ensuring stable flow temperatures and protecting the heat exchanger from thermal stress.

Why Do Some Heating Systems Need A Low Loss Header?

Some heating systems need a low loss header when there is a big difference between the boiler’s minimum flow rate and the variable demand from multiple heating zones, underfloor heating loops, large radiator circuits or when several boilers operate in cascade. Without one, boilers can short-cycle, overheat locally, lose efficiency or suffer premature component failure.

What Are The Main Benefits Of Installing A Low Loss Header?

The main benefits of installing a low loss header include improved boiler modulation and efficiency, reduced short-cycling, longer heat exchanger life, better temperature control across zones, easier integration of heat pumps or additional boilers, and more stable system pressure — all of which help maintain high ErP ratings and lower gas bills.

When Is A Low Loss Header Usually Recommended?

A low loss header is usually recommended for properties with:

• System boilers serving multiple heating zones
• Underfloor heating mixed with radiators
• Large homes or commercial buildings
• Cascade boiler setups
• Heat pump retrofits alongside existing gas boilers
• Any system where the boiler manufacturer states a minimum flow rate that exceeds typical zone demand

How Much Does A Low Loss Header Installation Cost In 2026?

A low loss header installation typically costs £800–£2,200 in 2026 depending on pipe diameter, insulation, labour, additional pumps/valves and whether it is fitted during a new boiler installation or retrofitted into an existing system.

Need A New Boiler Quote?

Adding a low loss header during a boiler replacement often delivers better long-term performance and protects your investment in a modern condensing boiler or hybrid system. 

Request a new boiler quote from Boilers 2 Go today — their qualified heating designers can evaluate your current layout and provide accurate pricing for a complete, efficient system that meets your needs as a homeowner or landlord.

FAQs

Can a low loss header be fitted to a combi boiler?

Combi boilers rarely need a low loss header because they supply on-demand hot water and heating without stored water or multiple zones — they are only added in unusual cases with very large or complex radiator circuits.

Does a low loss header improve my property’s EPC rating?

Indirectly yes — by allowing the boiler to modulate more effectively and reduce short-cycling, a low loss header can improve the SAP calculation and help achieve a higher EPC band, especially when combined with good controls and insulation.

Is a low loss header the same as a hydraulic separator?

Yes, the terms low loss header and hydraulic separator refer to the same component — the “low loss” name highlights the minimal pressure drop across the device.

Do I need extra pumps when installing a low loss header?

In most domestic installations one boiler pump is sufficient, but larger systems or those with underfloor heating zones often require secondary circuit pumps to ensure correct flow through each zone.

How does a low loss header help when adding a heat pump to an existing gas boiler system?

A low loss header allows the heat pump (which prefers lower flow temperatures and steady flow) to operate independently of the existing gas boiler circuit, enabling efficient hybrid operation without compromising either appliance.