Yes. An unvented hot water cylinder should be checked once a year by an engineer qualified to work on them, and most manufacturers make an annual service a condition of the warranty. These cylinders store hot water at mains pressure, so their safety valves need to work properly every time. The easiest approach is to have the cylinder checked at the same visit as your boiler service. We see plenty of unvented cylinders in larger homes around Westbury-on-Trym and Clifton.
What makes an unvented cylinder different
A traditional vented cylinder is fed by a cold water tank in the loft, so the pressure is low and limited by gravity. An unvented cylinder is fed straight from the mains. That gives you strong showers and no loft tank, but it also means the water inside is held under pressure while it’s being heated.
Because of that, unvented cylinders have several safety parts built in. They’re designed to release water safely if the pressure or temperature ever goes too high. Those parts only protect you if they’re working, and that’s why the annual check matters.
In England and Wales, installing an unvented cylinder falls under Part G of the Building Regulations, and the work should be done by someone with the right unvented hot water qualification.
What an unvented cylinder service usually covers
The exact checks depend on the manufacturer’s instructions, but a service generally includes:
- Testing the pressure relief valve and the temperature and pressure relief valve
- Checking the charge in the expansion vessel, which allows for water expanding as it heats
- Checking the incoming pressure reducing valve and cleaning its strainer
- Inspecting the tundish and discharge pipe to make sure they’re clear and run to a safe place
- Checking the thermostat and controls are working correctly
- Looking for leaks, corrosion or signs of overheating
The engineer should also fill in the service record in the cylinder’s paperwork. Keep it safe, as you may need it if you ever make a warranty claim.
Warning signs to look out for
You don’t need to wait for the annual visit if something seems wrong. These are safe things for any homeowner to keep an eye on:
- Water dripping or running from the tundish, the small open funnel on the discharge pipe, usually near the cylinder
- Hot water coming out of the discharge pipe outside
- Banging or hissing from the cylinder cupboard
- Taps spluttering or the pressure changing suddenly
- A damp patch or puddle under the cylinder
If you notice any of these, don’t try to adjust or take apart the valves. Turn the heating and hot water off if you’re worried, and call an engineer.
Why winter is a good time for the check
Hot water use goes up sharply in November and December. Longer showers, more baths and a house full of guests at Christmas all put the cylinder to work. If an expansion vessel has lost its charge or a valve is starting to let by, heavy use is when the problem tends to show itself. Getting it checked before the busy weeks gives time to order any parts.
Unvented cylinders in Bristol and Bath homes
Many larger period houses in Clifton, Redland and Bath have been modernised with two or three bathrooms, and an unvented cylinder is often how they get good pressure to every floor. In Bath, hard water adds another reason to stay on top of servicing, as limescale can build up on the cylinder’s heating parts and valves over time. If you’re also due a boiler check in the city, our boiler servicing in Bath page explains what we cover.
Frequently asked questions
Is an annual service a legal requirement for an unvented cylinder?
For a homeowner it isn’t a legal requirement in the way a landlord’s gas safety check is. However, most manufacturers require an annual service to keep the warranty valid, and the safety valves need regular checking to make sure they’ll work if needed. It’s sensible to treat it as an essential yearly job.
Can my boiler engineer service my unvented cylinder?
Often yes, if they hold the relevant unvented hot water qualification. Gas Safe registration covers gas work, not unvented cylinders, so it’s worth asking. Having both checked in one visit saves time and means one person has looked at the whole hot water system, from boiler to taps.
Why is my tundish dripping?
A dripping tundish means water is being released through one of the cylinder’s safety valves. It can be caused by a valve that’s worn, an expansion vessel that has lost its charge or a problem with the incoming pressure. It isn’t something to ignore. Call an engineer to find the cause and fix it properly.
Book your cylinder check
If your unvented cylinder hasn’t been looked at for a while, or the tundish has started dripping, give us a call on 01275 400 687 or drop us a message and we’ll check it over alongside your boiler.