If a boiler does not have hot water but the heating does, this can be due to several reasons. Join us in this article, because we will give you the causes and effective solutions to solve this type of breakdown. Towards the end of the article we offer you a table with the causes and solutions in summary form.
Causes ruled out if the hot water does not work from the boiler but the heating does
When the hot water does not work from the boiler but the heating does, there are some faults that can be ruled out because if they were the cause, there would be no heating either. So when the water does not work from the boiler but the heating does, problems such as:
- Clogged or broken circulation pump: The water that is heated in the boiler needs to be driven by a special pump which is designed for that purpose. The circulation pump is normally located inside the boiler and circulates the hot water to both the DHW and heating circuits. So if there is heating but no hot water, the circulation pump should not have a problem.
- Burner failures: Obviously, if the burner is clogged, dirty, or damaged to the point of not lighting, there will be no hot water for either DHW or heating. The same can be said about the elements of the ignition mechanism such as the electrodes, which may be dirty or misaligned, or the diesel pump (in the case of diesel oil boilers), which may be faulty.
- Dirty, clogged, or faulty fan. When a sealed boiler (including the condensing boiler) detects that the fan is not turned on and that the equipment is going to lack air for combustion and for the expulsion of residual gases, it stops and the burner does not turn on and no gas is generated. It’s the same with hot water. So if there is heating but no hot water, a problem with the fan can be ruled out.
It is better for a well-qualified technician to assess the specific situation of the boiler, but in general, we can say that the reasons we have just listed are ruled out when the boiler does not have hot water but the heating does.
The boiler does not work with hot water but the heating does
The following causes of breakdowns maybe those that are occurring when hot water does not work from the boiler but the heating does. Along with each cause, we will also show you the possible solutions.
Fault in the automatic ignition mechanism
If it is a boiler with flow technology, if any of the components of the automatic ignition mechanism (there are several) gets stuck or breaks down, hot water will not be generated. And since the 3-way valve remains in the heating position until there is a demand for hot water, there can be heating without hot water. The elements of the automatic ignition will have to be lubricated or replaced.
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But, and this is important: for the fault to be really located in the automatic DHW ignition system, it is necessary to check that the pipe that comes out of the 3-way valve towards the heating system is not hot and that it is not heating the radiators if the heating is off. Because if the radiators heat up with the heating off and the DHW on, then it is a fault in the 3-way valve, as we will see below.
The DHW does not work in the boiler until you turn on the heating
If the DHW does not work, but when you turn on the heating it starts to work, the reason must be that the circuits (heating and DHW) are connected. Normally both circuits must remain isolated from each other, even though they work with the same boiler. The main one in charge of managing the isolation and circulation of both circuits is the 3-way valve.
The most effective check, in this case, is to put into practice the opposite situation to that of the symptom, that is, turn off the heating, turn on the hot water, and check if the pipe that goes from the 3-way valve to the radiators is heated, and especially check if the radiators get hot. If so, this means either the 3-way valve is stuck and needs to be unstuck, repaired, and lubricated, or it is bad and possibly needs to be replaced with a spare.
Electronic board damaged
The electronic card acts as a brain that controls all the operations of the boiler. If it is broken, some processes cannot occur properly. If the water does not work in the boiler but the heating does, this may be a sign that the electronic card is faulty and must be replaced.
Table of causes and solutions for when DHW does not work but heating does
Let us now look at a summary table with the causes and solutions for when the hot water does not work from the boiler but the heating does. Once the reasons that cause neither the domestic hot water nor the heating to work have been ruled out, we can focus on the real subject of this article, which is when the hot water does not work in the boiler but the heating does.
| The boiler does not work hot water but the heating does | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| FAULT | SOLUTION | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Components stuck or damaged in the automatic ignition mechanism. | Clean, lubricate or replace the components of the automatic ignition (especially the membrane and the microswitch). | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 3-way valve stuck, dirty or faulty. | Clean, lubricate or replace the 3-way valve. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Faulty electronic card. | Replace the electronic card. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Frequently asked questions related to this topic
In this section we will concisely answer questions frequently asked by users of domestic boilers and heaters.
What to do when the heating does not work?
It is convenient to know what to do when the boiler does not heat. Some of these causes can be resolved by the user himself, but for most it will be necessary to request the services of a qualified technician.
| SYMPTOM | FAULT | SOLUTION |
|---|---|---|
| The heating does not work even if you try to turn it on. | The boiler is not in winter mode. | Select winter mode. |
| The boiler does not start. | Lack of gas or electricity. | Check if the bottle is exhausted or if there is a power cut. |
| DHW is generated when you turn on the heating. | 3-way valve stuck or faulty. | Unclog, lubricate or replace the 3-way valve. |
| The boiler does not start to maintain the programmed temperature. | Room thermostat faulty or incorrectly installed. | Replace the thermostat or install it correctly. |
| The programmed temperature drops due to lack of pressure. | Leaks in the heating circuit or in the radiators. | Detect and repair leaks. |
| The burner does not light and the boiler locks out. | Dirty or faulty burner, dirty, faulty or misaligned electrodes. | Clean or replace burner, or clean or align electrodes. |
| The radiators do not reach the programmed temperature. | Radiators with air or incrustations inside. | Bleed the radiators or clean them. |
| Why is there no hot water coming out of the heater? | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| SYMPTOM | FAULT | SOLUTION | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| The heater does not start. | Lack of fuel or electricity. | Check if there is gas in the tank or if there is a power cut. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| The burner does not light. | Fault in the automatic ignition mechanism. | Lubricate or replace the automatic ignition mechanism. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| The burner does not light. | Lack of water flow. | Clean the pipes, raise the water tank or install a booster pump. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| The water does not get hot enough. | Excess water flow. | Reduce the flow of water. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| The water does not get hot enough. | Dirty heater. | Purge heater. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| A specific tap does not generate hot water. | Local clogging of the tap or the surrounding pipes. | Unblock tap and pipes. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Electronic heater does not turn on. | Low batteries or dirty contacts. | Replace the batteries or clean their contacts. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
How to identify that the heating thermostat is not working?
First of all, make sure that the thermostat is installed correctly, before considering if it really may be faulty. There is also the option to restart it and everything may be resolved.
Finally, you can identify that the heating thermostat is not working whenever you detect the main symptom: the boiler works perfectly, but it does not comply with the on/off cycles to maintain the set temperature. In this case, the thermostat may need to be replaced.
