A heating expansion tank is the little tank, also known as the header tank or feed and expansion (F&E) tank, often located in the loft, above a boiler. This tank is filled directly from mains water. The header tank is separate from the cold water storage tank, as the header or expansion tank only feeds the central heating system.
Water flows down to fill the boiler and if the boiler needs to depressurise, water is pumped back up into the expansion tank. This allows the heating system to expand with heat.
If a radiator on the central heating system is drained down (perhaps to replace that radiator or replace thermostatic radiator valves), the expansion tank will automatically refill the system, filling the radiator back up. The expansion tank has a ballcock that will float in the tank, and when the water level reaches capacity, the ballcock will shut off the valve to no longer allow any more mains water to enter this tank. It is such a clever design, but like everything, it is prone to deteriorating with age and after a decade or more, this tank may need a plumber to repair or replace a part or replace the tank itself.
How do I know if my header tank for the central heating needs replacing?
The header tank is made of plastic and might need to be replaced every ten - fifteen years.
Reasons the header tank may need to be replaced include;
- if the header tank is prone to freezing during the winter months because it has not been properly insulated, this will lead to cracks and leaks
- the central heating system is pumping over a lot with hot sludge water, this might cause the header tank to eventually crack, needing to be replaced
- over the years, the plastic may become very brittle and just crumble if touched
- age deterioration might cause pinholes, leaking water in to the loft, which will eventually come through damaging the ceilings, if left
How much will it cost to replace a feed and expansion header tank?
The cost of removing an old feed and expansion tank and carrying out a replacement, plumbing in a new F&E tank will depend on the location of the tank and accessibility as well as what will be involved in the job. If the skilled plumber needs 30 minutes to clear a path from the loft hatch to the header tank, this will add to the cost of the job, so before calling the plumber in, make sure that the tank is accessible.
Image
Name
Cost
Byelaw 30 Tank Kit 4 Gallon + £10 18L Tank £35.00 
Polytank - Primary Expansion Cold Water Storage Tank 18L £42.00
If the expansion tank just needs a simple repair, e.g.; the overflow pipe has come loose and no longer correctly connected to the header tank, this might just result in an hours labour or a call-out fee plus minimal amount for materials.
If the plumber is isolating the existing header tank, and moving it to a new location, even upgrading the plastic tank itself, this can work out at a day or two labour charge. The exact time involved will depend on how challenging it will be to extend the pipework.
When you first contact the plumber, they will arrive and investigate, attempting to repair the tank or fix a valve first with replacement of the header tank being the last option. Removing the old deteriorated tank from the loft can turn into a challenge on its own, especially if it was metal rather than plastic. The header tank might need an electric saw or grinder (while being careful not to have any sparks set alight the roof trusses) to make the pieces of the tank small enough to discard through the loft hatch. To save money on labour charges, some plumbers may just leave the old discarded header tank, that is completely, isolated from the system, up in the loft, especially if you won’t be doing a loft conversion in the coming years.
|
Cost to repair or replace a header tank |
Per |
Average cost |
|
Replacing a ballcock valve in the header tank |
Per hour |
£45 |
|
Cleaning out the header tank |
Per hour |
£65 |
|
Moving the header tank to a new location |
Per day |
£280 |
|
Removing the header tank and isolating pipework |
Per day |
£260 |
|
Replacing the header tank |
Per day |
£290 |
Can my header tank be moved to a new location for a loft conversion?
Yes, a few ideas might be to convert the central heating system and replace it with a combi boiler so that the header tank is no longer needed. This will create a lot more space, eliminating the need for the header tank in the loft and housing a smaller boiler with no cylinder, potentially free’ing up a cupboard downstairs.
Or if the boiler is converted to a system boiler with a vented heat store tank with integral header tank, this can be situated anywhere, best being close to the boiler.
If you do not want to change the boiler system, then the header expansion tank can be relocated with the extension of pipework to a side of the loft conversion. This will free up the middle loft space, and the header tank can be neatly boxed in with some panelling. If you go for this option, do make sure that for any future issues with the header tank, that it will be easily accessible. The panelling should have an inspection hatch or window to keep an eye on it. You will need an easy way to remove the boxing, should you need full access to the tank in times of replacement or repair.
Can a header tank be repaired?
If you have noticed that your feed & expansion tank is slow to drain or filled with rusty sludge water at the bottom, this does not mean it needs replacing but rather a clean out and perhaps a powerflush to your central heating system. Most companies when powerflushing include a clean out the header F&E tank. This might be caused from years of the heating system pumping over into the F&E tank, sludge from the central heating system has deposited into the tank.
Sometimes the sludge can solidly block the cold feed pipe running down the expansion tank to the boiler, and this section of pipework might need cutting out and replacing.
If the tank is overflowing constantly running or filling up, the plumber might need to replace a faulty ballcock where the valve could be letting by or not closing correctly. Often the float mechanism is not rising to the correct level to shut off the water supply.
Reasons for the faulty valve not shutting off might be;
- The ballcock has a hole, filling with water so the ballcock is sinking and unable to close the valve, leaving the tank constantly refilling
- The rubber washer which seals off the valve has disintegrated through age and is not creating a watertight seal
- The brass nipple in the valve has deteriorated and no longer creates a seal, so the tank continues filling
This is an inexpensive part to change, as long as the plumber has access to the header tank in the loft.
The pressure inside the F&E tank can also cause the actual tank to degrade and may become perforated (pin-holes usually appear along the bottom or along the seam). A leak sealer may stop the leak, but this will only allow the tank to limp on for a while longer and should be replaced before any more damage is caused.