Bleeding radiators removes trapped air so radiators heat up at all, while balancing radiators adjusts valve flow to distribute heat evenly between radiators. Bleeding is included during boiler or cylinder installations, but balancing is a separate service and only carried out if specifically quoted.
Radiator balancing is a separate process that involves adjusting the hot water flow to each radiator so heat is distributed evenly throughout the property.
It is carried out by adjusting each radiator’s lockshield valve (typically the valve on the return side). This valve controls how much hot water is allowed to flow through each radiator.
Radiator balancing involves adjusting lockshield valves to control flow rates so that:
All radiators heat evenly between each other
No radiator “steals” heat from others, making some hotter and some colder
Balancing requires:
Time (it is done radiator by radiator)
Temperature measurements of flow and return
Multiple adjustments to each valve
System stabilisation after each change to confirm results
Radiator balancing is a standalone task, not a by-product of draining, refilling, bleeding radiators, or installing a boiler or cylinder.
Radiator balancing is not included in:
System drain-downs
Unless specifically quoted, the balance between radiators remains exactly as it was before the installation.
Radiator balancing is unrelated to fitting a boiler or cylinder
· It can take several hours to complete properly, depending on how many radiators there are in the property. The time required increases exponentially, not in a straight line.
· Balancing a small system (for example, 5–6 radiators) is relatively quick because adjustments are limited to a small number of radiators. However, as more radiators are added, each adjustment affects the entire system. Changing the flow to one radiator alters the balance across all others, meaning previously adjusted radiators often need to be rechecked and readjusted.
· On larger systems (for example, 15–20 radiators), radiator balancing will typically take around 4 hours and may require repeat visits. This is because the system needs time to stabilise after adjustments before temperatures can be accurately rechecked and further fine-tuning carried out.
· For this reason, balancing a large radiator system does not simply take “a bit longer” — it is a more involved, iterative process that must be done gradually to achieve correct results.
If radiator balancing is required, it must be quoted for and agreed separately.
Radiator bleeding means removing trapped air from radiators so hot water can circulate.
This is a basic necessity whenever a heating system is:
Drained down
Refilled
Opened for boiler or cylinder works
Bleeding simply ensures that radiators are able to heat up at all.
Included during boiler and cylinder installations
Required after draining the system
Does not control heat distribution
Does not improve system efficiency on its own
When we replace a boiler, we are simply replacing the heat source.
The boiler’s role is to generate heat and circulate hot water. It does not control how heat is distributed around the property – that function sits entirely with the existing radiator pipework and radiator valves.
During a boiler replacement:
The boiler (heat source) is replaced
Existing radiators are not altered, adjusted, or tampered with
Radiator valves and balance settings are left exactly as found
The way heat is shared between radiators remains unchanged
A successful boiler installation depends on the boiler functioning correctly — meaning it is able to heat water and circulate it around the system.
If radiators are heating up, this confirms the boiler installation is successful.
If the boiler were not operating correctly, none of the radiators would heat up at all.
The fact that some radiators are heating up demonstrates that:
The boiler is producing heat
The circulation pump is operating
Hot water is reaching the heating system
Individual differences in radiator temperature (some hotter, some cooler) have nothing to do with the heat source.
They are caused by existing pipework layouts and radiator valve settings, not the boiler.
If radiators were unevenly balanced before the boiler was replaced, they will remain unevenly balanced after — unless radiator balancing is specifically quoted for and carried out.
The same principle applies when replacing an unvented hot water cylinder.
A cylinder replacement relates only to domestic hot water storage (taps and showers). It does not alter:
Radiators
Radiator pipework
Radiator valves
Radiator balance
Replacing a cylinder has no impact on radiator performance or heat distribution.
As part of a boiler installation, the system will be chemically flushed using a recognised central heating system cleaner, such as Fernox F3, Adey MC3, or equivalent.
The process is as follows:
Cleaning chemical is inserted into the system (via the magnetic filter or a suitable dosing point)
The boiler is run so the system circulation pump moves the chemical through:
The boiler heat exchanger
Central heating pipework
Radiators
The chemical is left to work for approximately 1 hour, in line with manufacturer guidance
After the cleaning period, the system water containing loosened debris and light sludge is drained and replaced with fresh water
This process removes minor contamination and light debris only.
For a chemical flush to be effective:
The boiler must be operational
The system circulation pump must be functioning
Water must be able to circulate freely around the system
If the boiler is non-functional or unable to circulate water:
Cleaning chemicals cannot circulate correctly
The chemical flush will be ineffective
Sludge and debris will not be properly removed
A chemical flush:
Is suitable for systems in reasonable condition
Is typically included as part of a boiler installation
Is not intended to remove heavy sludge or resolve radiator cold spots
Where a system shows:
Persistent cold areas in radiators
Heavy magnetite sludge
Restricted circulation
A powerflush will be required.
A powerflush is a separate, specialist process, usually requiring a minimum of one full day, and is quoted separately.
Chemical flush = light system cleaning using Fernox F3, Adey MC3, or equivalent
Relies on normal system circulation
Boiler must be working
Not a powerflush
Heavy sludge requires a separately quoted powerflush
A powerflush is:
A minimum full-day job
Uses specialist equipment
Required when heavy sludge causes cold spots
Quoted separately
If radiators have:
Persistent cold areas
Heavy magnetite sludge
Poor circulation
A powerflush is required.
Symptom | Likely Cause | Solution |
Radiator cold at top | Air trapped | Bleeding |
Radiators heat unevenly | Flow imbalance | Balancing (quoted separately) |
Cold spots in radiators | Sludge buildup | Powerflush |
One radiator heats faster than others | Poor balance | Balancing |
20th August, 2026
18th March, 2026
