Heating Not Working After Summer? What to Check First
Turning the heating back on for the first time after summer is often when problems show themselves. The boiler may have been providing hot water normally for months, but when you ask it to heat the radiators again, nothing happens, only some rooms warm up, or the system starts making noises.
After more than 35 years working with heating systems, I would not immediately assume there is a major boiler fault. There are several simpler things worth checking first, and the way the system behaves can tell us a lot about where the problem is likely to be.
Check the thermostat and heating schedule first
Start with the controls. During the warmer months, the heating may have been switched off completely, left in a hot-water-only setting or programmed around a different schedule.
Turn the thermostat several degrees above the current room temperature and check whether the boiler responds. If you use a wireless thermostat, check the batteries too. It is also worth checking the date, time and heating schedule, particularly if there has been a power cut or the controls have been adjusted over summer. Boiler manufacturers recommend checking thermostat, programmer and heating settings when the system is not reaching the requested temperature.
If the boiler responds when you increase the thermostat but the radiators remain cold, that helps narrow the problem down further.
Check the boiler pressure
If you have a sealed heating system, look at the pressure gauge or digital display on the boiler.
The correct pressure varies between systems, so your boiler manual should always be the reference, but many sealed systems are around 1 to 1.5 bar when cold. If the pressure has fallen too low, the boiler may not operate correctly. Worcester Bosch and Vaillant both identify low system pressure as a possible cause of heating problems.
If you know how to repressurise your boiler safely, follow the manufacturer's instructions. However, if you top it up and the pressure drops again, repeatedly adding water is not the solution. Pressure loss can point to a leak or another fault within the heating system.
Are all the radiators cold or only one or two?
This is one of the most useful things to check.
If every radiator is cold, the problem may relate to the boiler, controls, pump or another part of the central-heating system.
If only one or two radiators are cold, while the rest of the house heats normally, the issue is more likely to be local to those radiators. That could include trapped air, a radiator valve, balancing or restricted circulation.
Knowing which pattern you have can save a lot of unnecessary fault finding.
Check the radiator valves
Thermostatic radiator valves, often called TRVs, control the flow of hot water through individual radiators.
Before winter, check that the valves have not simply been left turned down. If a radiator is completely cold while others are heating, the valve is one of the things worth looking at.
If the controls appear correctly set but the radiator still does not warm up, there may be a problem with the valve or circulation through that part of the system. Vaillant recommends checking radiator valve settings when individual radiators fail to heat.
Avoid forcing a valve or dismantling anything if you are unsure what you are doing.
Cold at the top? There may be air in the radiator
If a radiator is warm at the bottom but cold towards the top, trapped air is a common cause.
Bleeding the radiator releases that air and allows hot water to circulate through more of the radiator. You should switch the heating off and allow the radiator to cool before bleeding it.
After bleeding radiators, check the boiler pressure again. Releasing air and some water from the system can cause the pressure to fall.
If air keeps returning, however, I would want to understand why rather than simply continuing to bleed the radiators.
Cold at the bottom? It could be a circulation problem
A radiator that is hot at the top but noticeably colder at the bottom presents a different pattern.
Over time, rust, dirt and other debris can build up within a heating system and restrict the movement of hot water through radiators and pipework. Worcester Bosch identifies sludge and poor circulation as common causes of radiators remaining cold at the bottom.
Bleeding will not remove sludge from the bottom of a radiator. If several radiators are affected or the system is heating unevenly, it is worth having the system properly assessed before assuming a flush or any other treatment is required.
Is the boiler showing a fault code?
If the boiler is displaying a fault or error code, make a note of it.
The code can help identify what the boiler has detected, whether that relates to pressure, circulation, ignition, a sensor or another problem. Manufacturer fault-code information can often tell you whether there is a straightforward homeowner check or whether an engineer is required.
I would avoid repeatedly resetting a boiler that keeps returning to the same fault. A reset may get the appliance running again temporarily, but it does not fix whatever is causing the fault to return.
What if the boiler works for hot water but not the heating?
This is particularly useful information.
If you have a combi boiler and your taps and shower are producing hot water normally but the radiators will not heat, the boiler is clearly capable of producing heat. The problem may instead involve the heating controls, circulation or a component such as the diverter valve, which directs heat between the hot-water and central-heating sides of a combi boiler.
This type of fault often becomes noticeable when the heating is switched back on after a long period of only using the boiler for hot water.
It needs proper diagnosis rather than assuming the boiler itself needs replacing.
What can you safely check yourself?
Before calling an engineer, I would check:
The thermostat is switched on and calling for heat
The heating schedule and clock are correct
The boiler is not set to hot-water-only or summer mode
Wireless thermostat batteries are working
Boiler pressure is within the manufacturer's recommended range
Whether all radiators are affected or only one or two
Radiator valves are open
Whether radiators are cold at the top, bottom or completely cold
Whether the boiler is displaying a fault code
Those checks can often either solve a simple issue or give an engineer much better information about what the system is actually doing.
When should you call an engineer?
I would have the heating system checked if the boiler does not respond when the thermostat calls for heat, all of the radiators remain cold despite the controls being correctly set, the pressure repeatedly falls, a fault code keeps returning or the system is making unusual noises.
The same applies if individual radiators still will not heat after the straightforward checks, or you suspect a problem with the pump, valves or components inside the boiler.
Do not remove the boiler casing or attempt repairs to gas components yourself. Gas appliance work should be carried out by an appropriately qualified Gas Safe registered engineer.
The first cold spell is not the time you want to discover that a small problem has been sitting unnoticed all summer. If something does not seem right when you first switch the heating back on, getting it checked early can prevent you being left without heating when you need it most.
Local help in West London
West Gas Service provides gas, heating, plumbing and air conditioning services across West London, Surrey and surrounding areas. With more than 35 years of experience, we regularly diagnose boiler and central-heating problems, from low pressure and cold radiators to control, circulation and component faults.
If your heating is not working properly after summer, we can diagnose the problem, explain your options clearly and recommend the work that is actually needed.
Call 07866 567112, email ralphwestgas@gmail.com, or submit a form and a qualified engineer will be in touch.
