Boiler fault guide for North East homes
No Hot Water but Heating Works? What to Check
If you have no hot water but the heating works, the boiler can clearly produce heat, but something is stopping that heat reaching your taps or stored-water cylinder. With a combi boiler, a diverter valve or hot-water demand sensor may be involved. With a system or regular boiler, check the hot-water controls first. You can make a few safe observations without removing the boiler casing.
Start with the pattern, not a guess
A cold shower does not automatically mean you need a new boiler. The useful clues are which outlets are affected and what the boiler does when you open a hot tap.
Try more than one hot outlet. If the kitchen tap runs hot but the shower stays cold, the problem may be local to the shower valve. If hot and cold taps are both dry, check for a supply interruption. If cold water flows normally but every hot outlet remains cold, focus on the boiler or stored-hot-water system.
60-second decision helper
What best describes your hot-water problem?
Choose the closest match. This cannot diagnose a fault, but it will help you decide which safe check to make and what to tell an engineer.
No hot water but heating works: likely causes
The system type changes the shortlist. A combi makes hot water on demand, while a system or regular boiler normally heats water stored in a cylinder. That distinction is more useful than the boiler brand at the start of fault-finding.
Controls or programmer settings
A power cut, flat controller battery, clock change or accidental adjustment can alter the hot-water schedule. This is especially relevant where a cylinder has separate heating and hot-water programmes. Check that hot water is enabled and the date and time are correct.
Combi diverter valve fault
A combi must direct heat towards either the radiators or domestic hot water. If its diverter valve sticks in the heating position, the radiators can work while taps remain cold. The valve sits inside the appliance, so diagnosis and repair belong to a competent Gas Safe engineer.
Hot-water flow sensor or thermistor
A combi must recognise that a tap has opened and control the outlet temperature. A failed flow sensor may not register demand; a temperature-sensor fault can cause erratic operation. An engineer can test rather than replace parts by guesswork.
Plate heat exchanger restriction
In many combis, a plate heat exchanger transfers heat into the tap-water side. Scale or debris can restrict that transfer, causing lukewarm or fluctuating water. Water conditions and the exact symptom matter to the diagnosis.
Cylinder thermostat or zone valve
On a stored-water system, the boiler may heat the radiators perfectly while a programmer, cylinder thermostat, motorised valve or related control stops the cylinder receiving heat. The immersion heater, if fitted, is a separate system and should only be used according to its instructions.
Pressure, lockout or another boiler fault
Low system pressure or a displayed fault code can affect operation, although pressure requirements vary by model. Record the exact code and gauge reading. One reset may be appropriate if the manufacturer’s manual says so; repeated resetting hides the symptom without fixing its cause.
| What you notice | Where to look first | Sensible next step |
|---|---|---|
| All hot taps flow normally but stay cold | Hot-water setting, demand indication, fault code | Check controls and manual; book fault-finding if unresolved |
| One shower or tap is cold | That outlet, mixer cartridge or local valve | Compare other outlets before assuming a boiler fault |
| Water alternates hot and cold | Flow rate, sensors or heat transfer | Note when it happens and arrange diagnosis if persistent |
| Cylinder is cold but radiators heat | Hot-water programme, cylinder thermostat, zone valve | Check settings; use a qualified engineer for electrical or valve work |
| No flow from hot or cold taps | Incoming water supply or isolation | Check the supplier and accessible stop tap; seek plumbing help |
Safe checks before booking a boiler repair
- Try two or three outlets.Note whether the problem affects every hot tap, only the shower or one room. Also compare hot-side flow with cold-side flow.
- Read the display without opening the boiler.Photograph the fault code, pressure reading and any warning light. Check the model-specific manual rather than relying on a generic reset sequence.
- Check the accessible controls.Confirm hot water has not been turned off, and that the programmer shows the correct time. For a cylinder, check the hot-water channel as well as the room-heating channel.
- Check for an obvious supply interruption.If cold taps are also affected, ask neighbours or check your water supplier. If the boiler display is blank, check for a wider power cut and the normal household controls you are competent to use.
- Observe what happens when a hot tap opens.Does the boiler display change? Does a flame symbol appear? Does it start and stop? You are gathering evidence, not touching internal components.
- Stop if anything looks unsafe.Leaks near electrical parts, signs of overheating, combustion smells, gas smells or a CO alarm require immediate safety action, not more troubleshooting.
Do not remove the front casing, interfere with gas valves, dismantle a diverter valve or test live electrical components. HSE states that anyone employed to work on a domestic gas appliance must be Gas Safe registered and competent for that work.
What to tell the engineer
A clear description can shorten the path to a useful diagnosis. Before contacting Enerus, make a note of:
- the boiler make, model and approximate age;
- whether it is a combi or works with a hot-water cylinder;
- the exact fault code and pressure reading;
- whether every hot outlet is affected;
- whether the water is completely cold, lukewarm or intermittent;
- what the boiler display does when a hot tap opens; and
- when the problem started and whether anything changed beforehand.
A photo can help, but it does not replace an on-site test. Good fault-finding confirms the problem before chargeable work is agreed.
Repair, service or replacement?
No hot water is a repair symptom, so book a boiler repair rather than a routine service. An annual boiler service is preventive maintenance; it is not designed to absorb the time and parts needed to investigate an active breakdown.
One fault does not automatically justify replacement. The decision depends on the diagnosis, repair cost, boiler age, condition and parts availability. If the appliance repeatedly fails or no longer suits the household, compare a documented repair with a properly scoped new boiler quotation.
For future maintenance, Enerus also offers annual boiler service plans. These are maintenance memberships, not breakdown insurance, so repairs, parts and call-outs are not automatically included.
Why North East homes can present different clues
Across County Durham, Newcastle, Sunderland, Gateshead, North Tyneside, Northumberland, Darlington and Teesside, homes range from flats with combis to older properties with stored hot water. The same symptom can therefore point to a different component.
In a combi-equipped flat, working radiators and normal cold flow focus attention on hot-water demand and switching. With a cylinder, programmers, thermostats and motorised valves add other possibilities. Similar symptoms have different causes, which is why an engineer should test rather than assume.
Enerus provides boiler fault-finding across the North East, subject to postcode and availability. Share your location, system type and symptoms when you enquire so the team can confirm the appropriate appointment.
Frequently asked questions
Why is my heating working but I have no hot water?
The boiler or heating source can still produce heat, but the hot-water side is not receiving or transferring it correctly. With a combi, possible causes include controls, a flow sensor, diverter valve, temperature sensor or plate heat exchanger. With a cylinder, the programmer, thermostat or motorised valve may be involved. These are possibilities, not a diagnosis.
Can I fix a diverter valve myself?
No. The diverter valve is inside the boiler and should be diagnosed and repaired by a competent Gas Safe engineer. Removing the casing or trying to manipulate internal parts is not a safe household check.
Should I reset the boiler?
Only follow the reset procedure in the manual for your exact model, and do not keep resetting a boiler that locks out again. Record the code before resetting. A recurring lockout needs investigation.
Why does hot water start warm and then turn cold?
Fluctuating temperature can relate to water flow, sensing, control or heat-transfer problems. Check whether it happens at every outlet and whether reducing the tap flow changes the symptom, then give those observations to the engineer.
Why is only my shower cold?
If other hot taps work normally, the boiler is producing hot water. A shower mixer, cartridge, local valve or flow issue is more likely than a complete boiler hot-water failure. A plumber or shower specialist may be the appropriate first call.
Is no hot water an emergency?
It is urgent for many households, but it becomes a gas-safety emergency if you smell gas, suspect unsafe combustion, see scorching or a CO alarm sounds. In that situation, stop using the appliance, ventilate the property and call 0800 111 999.
Still have no hot water? Let’s identify the fault
Tell Enerus what works, what does not and what the boiler display shows. We will help confirm the right next step and, where appropriate, arrange professional boiler fault-finding in your part of the North East.