Boiler fires, radiators stay cold
Water isn't circulating: a seized or failed pump, or a zone valve stuck shut.
Pump & zone valve replacement
Heating on, radiators cold? It's often the pump or valve.
Failed circulating pumps and sticking 2-port and 3-port zone valves are some of the most common heating faults. We diagnose them properly and replace only what's actually failed.
Gas Safe registeredS-plan & Y-plan systemsHigh-efficiency pumps
Symptoms
Signs of a pump or zone valve fault
Hot water but no heating (or the reverse)
The classic zone valve fault. The motor, microswitch or spindle has failed.
Humming, grinding or rattling
Worn pump bearings, air in the pump, or debris from sludge.
Only some zones work
On S-plan systems, one 2-port valve failing leaves that zone cold.
Pump hot but not pumping
A seized shaft, common after the heating has been off all summer.
Boiler overheating or kettling
Poor circulation means heat can't get away from the boiler fast enough.
The science
Why pumps and valves fail, and what a modern one saves
Pumps and valves sit in your heating water all year, so the condition of that water decides how long they last.
EEI ≤ 0.23
Efficiency rules
Since August 2015, standalone circulating pumps must meet an Energy Efficiency Index of 0.23 or better.
Source: Ecodesign Regulation (EC) 641/2009, as amended by 622/20125 W
Modern pump, low demand
The ALPHA2 in our photo was drawing just 5 watts. Variable-speed pumps slow down when demand is low.
Source: on-site reading, Grundfos ALPHA2 15-6045–100 W
Older fixed-speed pumps
Older 3-speed pumps typically run at a fixed 45 to 100 watts, whatever the demand.
Source: manufacturers' published ratingsFe₃O₄
Magnetite sludge
Black iron-oxide sludge is abrasive and magnetic. It collects in pump rotors and wears them out.
Source: BS 7593 water treatment guidance2-port vs 3-port valves
A 2-port zone valve (S-plan) simply opens or closes one circuit. A 3-port mid-position valve (Y-plan) directs water to heating, hot water or both from a single valve. When the motor or its internal switch fails, the boiler either never gets the call for heat or the water goes the wrong way, which gives the classic "hot water but no heating" fault.
Worked example: swapping a 60 W fixed-speed pump for a variable-speed one averaging 10 W saves around 100 kWh over 2,000 running hours a year.
How it works
Diagnose, replace, protect
Test the circuit
We check controls, wiring and valve operation to find exactly what's failed.
Price before work
Head only, full valve or pump: you'll know which and what it costs.
Replace and bleed
New parts fitted, air bled out, circulation and controls tested.
Protect it
If sludge caused it, we'll recommend a clean and filter so it doesn't happen again.
FAQs
Pump and zone valve questions
Can you replace just the zone valve head?
Often, yes. On many 2-port valves the motor head (actuator) unclips from the valve body, so it can be swapped without draining the system. If the valve body or spindle has seized, the whole valve is replaced.
Does the system need draining to change a pump?
Not always. If there are working isolation valves either side of the pump, it can be changed with minimal water loss. If not, we drain down and fit new valves so next time is easier.
What's the difference between S-plan and Y-plan?
S-plan uses a separate 2-port valve for each zone, such as heating and hot water. Y-plan uses a single 3-port mid-position valve to send water to heating, hot water or both. Both are common. The symptoms of a fault are similar, but the fix is different.
Why did my pump fail?
The usual causes are sludge (magnetite) wearing the pump, air in the system, a seized shaft after a summer off, or simple age. If sludge is the cause, cleaning the system and fitting a magnetic filter protects the new pump.
Is a new pump more efficient?
Usually, yes. Since 2015, standalone heating pumps sold in the UK must meet strict efficiency rules. Modern variable-speed pumps adjust to demand and can use a fraction of the electricity of older fixed-speed models.
Sources and standards referenced
- Commission Regulation (EC) No 641/2009, as amended by (EU) No 622/2012 (ecodesign for circulators)
- Grundfos ALPHA2 product data
- BS 7593:2019, treatment of water in domestic hot water central heating systems
Areas covered
Pump and zone valve replacement across Trowbridge and West Wiltshire
Based in Trowbridge, covering a 25-mile radius. Not sure if you're covered? Call and ask.
TrowbridgeBathBristolSwindonFromeYeovilBradford on AvonMelkshamWestburyWarminsterDevizesChippenham