Biasi Boiler No Hot Water: Causes and What to Check
A Biasi boiler with no hot water but working heating almost always has a fault in one of three parts: the diverter valve, the hot water flow switch or the plate heat exchanger. If the heating has stopped as well, or a lockout light is showing, check the pressure gauge and the gas supply first, because low pressure and a failure to light stop everything. Biasi combis such as the Riva Plus, Riva Compact, Garda and Parva were fitted in a great many London flats and conversions, and most are now well into their working lives. They are still repairable in most cases, but parts can take longer to source than for the most common brands, so it helps to know what you are dealing with before anyone orders anything.
Which Biasi do you have?
The model name is usually printed on the front panel or on a data badge behind the lower cover: Riva Plus HE, Riva Compact HE, Garda HE, Parva HE, Inovia and Activ are the names we see most in London. Nearly all of them are combis, meaning the hot water is heated inside the boiler the moment you open a tap, with no cylinder in the airing cupboard.
If you do have a hot water cylinder, you have a system or heat only boiler, and the fault may be in the controls or valves outside the boiler. Our guide to no hot water but the heating works covers those set-ups. The rest of this page assumes a Biasi combi.
Heating off too? Start here
If nothing works, the boiler has usually locked out. Depending on the model you will see a red light, a flashing symbol or a code on a small display. Note what it shows before pressing anything, because a reset clears it.
- Pressure: the gauge on the front should read around 1 to 1.5 bar with the boiler cold. Below that, most Biasi combis will not fire. Top it up through the filling loop as your manual describes.
- Gas: light a hob, if you have one, to prove the supply, and check a prepayment meter has credit.
- Power: check the fused spur next to the boiler is on and nothing has tripped at the consumer unit.
- Condensate: in freezing weather, the plastic pipe running outside can freeze and stop a condensing Biasi. Thaw it with warm, not boiling, water.
- Reset: press the reset button once and wait a couple of minutes. Our guide on how to reset a boiler explains why you should stop after two tries.
Heating works but no hot water
With radiators heating normally and no lockout, the boiler is lighting fine. It is just not switching over to make hot water, or not heating the water once it does.
The diverter valve decides where the boiler's heat goes. On many older Biasi combis this is a water operated assembly with a rubber diaphragm, rather than a motorised valve, and the diaphragm hardens and splits with age. When it fails, the boiler keeps heating the radiators even with a hot tap open. Our guide to diverter valve replacement cost explains what is involved.
The flow switch tells the boiler a tap is open. When it sticks, often because of scale or a tired microswitch, the boiler stays silent as you run the hot tap. A useful clue: if the boiler does not fire at all when you open a hot tap, but does fire for the heating, the flow switch or diverter is the first suspect.
The plate heat exchanger passes the heat to your tap water. In London's hard water, it gradually scales up, and on a boiler of this age it is often well furred. Hot water that starts warm and fades, or that never gets properly hot even with the temperature turned up, points here. Our guide to a blocked plate heat exchanger explains how it is confirmed.
Lukewarm water, or hot then cold
Water that only gets lukewarm while the radiators warm up at the same time usually means the diverter is sitting partway, sending some heat each way. Water that runs hot and then cold with the tap left open is more often a flow problem. Open the tap fully first, because a low flow can drop below what the boiler needs to stay lit. If a full flow still swings, scale in the plate heat exchanger or a sticking flow switch is the usual cause. Our page on no hot water from a combi boiler goes through the same three parts on other makes.
Parts, age and the repair or replace question
Biasi boilers have not been a common choice for new installations in the UK for some years, so fewer engineers carry the parts and some are only available to order. Diverter assemblies, flow switches and plate heat exchangers for the popular Riva and Garda models can usually still be found, but it is worth confirming before a visit rather than after.
Whether to repair depends on what else is wrong. A boiler that is otherwise in good order, with one failed hot water part, is normally worth fixing. A boiler with a corroded heat exchanger, repeated faults, or a part that cannot be sourced is a different conversation. A boiler diagnosis gives you that answer in writing, and if replacement does make sense, our boiler replacement page explains how we approach it. Our guide to boiler brands to avoid also explains why parts support matters as much as build quality.
Taking the case off a gas boiler is gas work and must be done by a Gas Safe registered engineer. That includes the diverter, the flow switch and the plate heat exchanger. If you smell gas, turn it off at the meter, open the windows and call the gas emergency line on 0800 111 999.
When to call us
Call us on 020 4652 5111 or send an enquiry if the boiler locks out again after a reset, the pressure keeps dropping after you top it up, water is dripping from the boiler or the pipes under it, or the hot taps still run cold after the checks above. Tell us the model name on the front so we can check parts before we arrive. We have 20 engineers across London, and our rate is on the pricing page, agreed before anyone attends.
Questions we get asked
- Why is my Biasi boiler not giving hot water but the heating works?
- The usual causes are a diverter valve or diaphragm that no longer switches to hot water, a flow switch that does not register the tap, or a plate heat exchanger clogged with scale. All three need a Gas Safe engineer to diagnose and replace.
- How do I reset a Biasi boiler?
- Most Biasi combis have a reset button or a reset position on the mode selector. Press or turn it once and wait a couple of minutes. If the lockout returns, the cause needs finding rather than more resets.
- Can you still get parts for a Biasi boiler?
- For the common models, such as the Riva Plus and Garda, most hot water parts can still be sourced, though some need ordering. For rarer or older models it is worth checking availability before committing to a repair.
- Is it worth repairing an old Biasi Riva?
- Often, if the boiler is otherwise sound and the failed part is available. If there are repeated faults, corrosion or parts that cannot be found, replacement is usually the better use of money. A diagnosis visit answers that properly.
- Why is my Biasi hot water only lukewarm?
- Usually the diverter is stuck partway, sending some heat to the radiators, or the plate heat exchanger is scaled up and cannot pass enough heat to the water. Check whether the radiators warm up while the hot tap runs.