If your combi boiler heats the house but the taps stay cold, the working heating is a useful clue—not a diagnosis of the hot-water fault.
Start by identifying whether the problem affects one fixture or every hot-water outlet, and whether you actually have a combi appliance or a boiler connected to a separate tank. This guide explains what to observe safely, what a professional assessment should separate, and what to tell SkyLimit when booking in Metro Vancouver or the Fraser Valley.
Have the brand, model, city and any displayed message ready. For the reverse symptom, use our combi boiler hot water but no heating guide.
First confirm what heats your tap water
A combi boiler provides space heating and domestic hot water. A heating-only boiler may instead serve an indirect hot-water tank, while another home may have a completely separate tank or tankless water heater. These layouts can look similar in a mechanical room, but they need different fault investigations.
Read the model from an accessible label without opening the appliance. Note whether there is a storage tank nearby and whether you know which appliance supplies the taps. A brand name on its own is not enough: one manufacturer can sell heating boilers, combi boilers and water heaters with different controls and components. Our combi boiler versus indirect water heater comparison explains the layout choices.
If there is a separate domestic water heater, the heating boiler may be operating normally while the other appliance needs attention. Describe both pieces of equipment when requesting water heater repair. In a strata property, also establish whether hot water comes from equipment inside your unit or a shared building system before arranging access.
Compare the symptom before assuming a boiler failure
Use observations from ordinary use. Do not keep running a faulting appliance, deliberately provoke overheating or create repeated test cycles. The purpose is to describe the complaint accurately, not to identify a replacement part yourself.
| What you notice | Why the distinction matters | What to report |
|---|---|---|
| One shower is cold, but other taps get hot | The fixture or its local mixing control may need assessment. | Which outlet fails and which outlets still work. |
| Every hot-water outlet stays cold | The common hot-water source, its demand response and shared plumbing need consideration. | Whether water flows normally and whether the boiler display changes during normal use. |
| Water starts hot, then becomes cold | An intermittent demand, control, heat-transfer or delivery problem may be involved. | How long the pattern lasts and any displayed message. |
| Hot water weakens when another outlet opens | Simultaneous demand and available delivery capacity become relevant. | Which fixtures were running and whether this behaviour is new. |
| Neither hot nor cold taps have normal flow | A wider water-supply interruption may be part of the complaint. | Whether neighbours or building management report the same issue. |
Warm radiators or floors may retain heat after the boiler stops firing. When you say “heating works,” explain whether the home is maintaining temperature normally or whether you only noticed a warm pipe. That distinction helps avoid treating stored warmth as proof that the appliance is currently operating.
Useful checks that do not involve opening the boiler
- Record the display. Take a clear photo of the exact code or message and note when it appeared. Do not erase the evidence by repeatedly resetting the unit.
- Describe normal water use. Note whether the kitchen, bathroom basin and shower are all affected. Avoid putting your hands under unexpectedly hot water.
- Review familiar user settings. Consult the owner manual for the exact model to see whether domestic hot water is enabled and whether a user schedule applies. Leave installer menus and wiring alone.
- Note the timeline. Did the problem begin suddenly, gradually, after a power interruption or after plumbing or appliance work? A timeline is evidence, not proof that the recent work caused the fault.
- Look from a safe distance. Report visible water around the appliance or obvious external damage. Do not touch wet controls or remove panels to improve the view.
Do not raise temperatures to force hot water, open a filling valve, bleed the system or apply a pressure target found for another model. The heating-circuit gauge does not measure tap-water temperature or confirm hot-water delivery. The correct operating guidance depends on the installed appliance and system.
In a shared building, contact the property manager if the supply arrangement is unclear or other units are affected. Tell the booking team about access requirements and any work that needs coordination with building management.
What a technician needs to distinguish
Hot-water demand is not the same as a room-heating request
A working room thermostat tells you little about how the appliance recognizes water use at a tap. The assessment should establish whether the actual model sees a domestic-hot-water request, whether its controls respond, and whether the observed behaviour matches its documentation. A missing response does not automatically identify a failed sensor; water flow and the connected arrangement also matter.
Heat must reach the domestic water
Manufacturers use different designs to provide heating and domestic hot water. For example, Navien documents a dedicated domestic-hot-water heat exchanger on its NCB700 series. That example explains why successful space heating does not verify every hot-water component. It is not a parts diagram for every Navien or other-brand boiler.
A professional should use the model-specific sequence to investigate the relevant heat-transfer components, sensors and controls. A diverter or switching component is a possibility only where that design uses one. Do not approve a part solely because an online symptom list names it. Ask what observation or test supports the recommendation and whether the proposed part matches the model and revision.
Hot water must also arrive correctly at the fixture
Temperature control and mixing in the plumbing can affect what reaches the taps. If other outlets work, that local evidence matters. If the complaint occurs only with several fixtures running, the assessment should consider demand and delivery conditions rather than immediately declaring a failed boiler. An indirect-tank installation needs its own tank demand and heat-delivery checks.
For brand-specific booking information, see Navien boiler repair or Viessmann boiler repair. The gas boiler parts guide explains why identification and compatibility matter before ordering components.
Repair, maintenance or replacement?
An active loss of hot water is a repair complaint. Tell the company about it before booking gas boiler repair, even if you also want an annual visit. Routine boiler service and maintenance has an agreed scope; it should not be assumed to include diagnosis and repair of every connected plumbing issue.
Replacement is a separate decision. Ask for the diagnosed cause, available repair options, component availability and the condition of the existing equipment. If inadequate hot-water delivery is a long-standing concern, discuss the household’s simultaneous demand and installed layout. A larger appliance should not be selected from floor area or a symptom alone. Our boiler installation guide covers project planning.
After agreed work, ask whether domestic-hot-water delivery was checked under the relevant conditions and whether space heating also operates as intended. Keep the service findings and model details for future visits. An explained result is more useful than a generic statement that the boiler was “serviced.”
What to send when requesting an assessment
- Your city and whether the equipment is in a house, suite or shared mechanical room.
- An accessible brand/model label and a clear photo of the display.
- Whether a separate storage tank or water heater is present.
- Whether all taps are affected, or the problem is limited to one fixture.
- Whether water is always cold, changes temperature or fails during simultaneous use.
- Any recent work, interruption, leak or recurring fault message.
Send equipment photos through the booking method agreed with the company. Avoid including unrelated personal documents or occupants in the frame. Call 778-892-5119 to discuss the symptom and appointment availability.
Questions about heating working but no hot water
Why do I have heating but no hot water from my combi boiler?
The space-heating and domestic-hot-water functions have different demands and water paths. Working heating does not confirm hot-water demand detection, heat transfer or delivery to the taps. Check whether every outlet is affected and record the display before arranging a model-specific assessment.
Does no hot water always mean the diverter valve has failed?
No. Not every combi uses the same internal arrangement. Demand detection, sensors, heat transfer, controls and plumbing mixing can produce similar symptoms. A technician should confirm the cause and the correct component for the exact model before recommending a replacement.
Why is only my shower cold when other taps are hot?
A problem limited to one shower may be associated with that fixture, its cartridge or local mixing controls. Tell the technician which other outlets work normally. A cold shower alone does not establish a boiler fault.
Why does the hot water go cold when another tap opens?
The pattern may involve simultaneous demand, available flow, temperature rise or mixing. Record which outlets were in use and whether the problem is new. It does not by itself prove that the boiler needs replacement.
Can I fix this by turning up the room thermostat?
A room thermostat normally requests space heating. Turning it up does not establish a repair to the domestic-hot-water function. Use the exact owner manual for familiar user settings; leave installer settings and internal work to a qualified professional.
Should I reset the combi boiler if the heating still works?
Record any fault code before taking action. Follow only the owner instructions for the exact model, and do not repeatedly reset a recurring or unexplained fault. Stop using the equipment and seek help if there is a safety concern.
Is an indirect hot-water tank the same fault as a combi boiler?
No. An indirect tank stores domestic hot water and uses a connected boiler circuit to heat it. Tank demand, its controls and heat delivery may need assessment even while the home is warm. Tell the service company that a separate tank is present.
Will routine boiler servicing automatically restore my hot water?
Routine maintenance and diagnosis of an active fault have different scopes. Report the hot-water failure when booking so the visit can address the complaint. Ask what was found and whether hot-water delivery was verified after the agreed work.
Published by SkyLimit Heating and Gas Ltd.
This guide helps homeowners describe a domestic-hot-water complaint and prepare for an assessment. It does not diagnose a particular appliance or replace its owner instructions. See the gas boiler guide for heating types, related problems and service options.
Technical references: Navien NCB700 manufacturer information; Viessmann’s overview of no-hot-water causes. Appliance arrangements vary; use Canadian documentation for the installed model. UK-specific pressure targets and professional-registration rules are not instructions for a BC installation.
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