Asked by: Debbra Weilandt
home and garden home appliances

Why does my boiler go hot and cold?

Last Updated: 29th June, 2020

Combi boilers are a lot more reliable than they were ten years ago. However, combi boilers are prone to the common problem of causing the hot water to go cold or lukewarm and then back to hot again. Symptoms like these are usually signs of a blockage in the hot water heat exchanger in the boiler.

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Beside this, why does my hot water temperature fluctuate?

Adjust the thermostat brackets if necessary to keep the thermostats snug against the tank. A failed thermostat or heating element in an electric water heater can also cause hot water temperature fluctuations. Sediment build-up at the bottom of the tank can cause hot water temperature fluctuations.

Also Know, why is my boiler overheating? Typically, boilers overheat due to the failure of safety controls that maintain the gas and water supply, the temperature and the pressure. In some cases, this can lead to a condition called a 'runaway boiler', which is very dangerous to both occupants of the property and emergency service responders.

Consequently, why does my combi boiler run out of hot water?

If your home runs on a combi-boiler, then low pressure may be the reason for your lack of hot water. The water pressure for a standard domestic boiler is usually around 1.5 bar and will be displayed on a gauge known as a 'Manometer', usually located where the water supply pipes are connected to the boiler.

How do you adjust a hot water temperature control valve?

To adjust the mixed outlet temperature of the valve, remove the cap to gain access to the adjusting spindle. The spindle should be rotated-clockwise to reduce the temperature, counter-clockwise to increase the temperature until the desired set point is reached.

Related Question Answers

Remedio Ruiz De Castroviejo


Why does shower water go hot then cold?

The shower would get cold if somebody used hot water for something (almost certainly not a toilet flush), instead of cold. It could be caused by an over-enthusiastic thermostatic mixing valve, which reduced the hot water flow too much. Using up all the water in the hot water tank would also lead to a cold shower.

Marvis Schwindenhammer


How do I adjust my shower mixing valve?

Adjust the Shower Valve
  1. Remove the handle. You may need a screwdriver to do this.
  2. Take off the metal cover beneath the handle, exposing the valve stem.
  3. Turn the RSL two notches in whichever direction desired, then put the RSL back in place.
  4. Replace the faucet handle, then test the mixture of hot and cold water.

Cherry Pekhotin


How do you increase your water pressure?

Make sure the shutoff valves near the water meter are fully open. Sounds basic, but plumbers still have to charge for a service call to simply turn a water pressure valve handle! Then check the water pressure. If your house is on city water, ask your local water department for a pressure reading.

Arafa Rudalf


Why is my hot water not consistent?

If your hot water heater does not keep a constant temperature, you may have a defective thermostat. The upper control thermostat controls power to the upper element, and as well, is used to divert power to the lower thermostat and heating element when the correct temperature at the top of the tank is reached.

Bernhard Moskowitz


What to check when there's no hot water?

Need to hire a plumber?
  • No Hot Water – Electric Water Heaters. Faulty Heating Element. Faulty Thermostat. Tripped Circuit Breaker. Other Causes of Hot Water Not Working:
  • No Hot Water – Gas Water Heaters. No Gas Supply. Pilot Light is Out. Thermocouple.
  • Water is Not Hot Enough. Check Thermostats. Inspect Burner. Examine Dip Tube.

Souraya Padro


Can I run 2 showers from a combi boiler?

*However combi boilers do not cope well with 2 showers running at the same time in the same property, due to the use of hot water across both showers. The good news though is that you will no longer need a hot water cylinder or a cold water tank in the loft space, roof or basement though.

Bahri Adelina


What should boiler pressure be when heating is on?

What pressure should my boiler be? Generally, your boiler pressure should be between 1 and 2 bar. However, read your boiler's manual or ask your heating engineer for the required pressure for your particular model. To check your boiler's pressure, you need to locate the pressure gauge on your boiler.

Touriya Ikusa


How do I fix no hot water pressure?

If you still have low hot water pressure the problem may be the supply line under the sink. Remove the line from the shut-off valve and the bottom of the faucet and clean or replace it. Also check the pressure coming out of the shut-off while you have the supply line off.

Lamberto Echaburu


Why is my boiler not firing up?

The boiler not firing might be due to thermostat being set too low. The heating system will not start until its environment temperature is below the level set on the boiler system. Increase the thermostat to a higher level and hopefully this will solve the reason why your boiler is not firing.

Sokayna Tchekmenev


Does boiler pressure affect hot water?

Low pressure can be a cause of many heating niggles if you have a sealed system or combi boiler. This is the type of boiler which does not have an additional tank in the loft. If your hot water pressure is low all of a sudden, check the pressure gauge on your boiler, which should be set at around 1 bar.

Yanfang Mewes


How do I know if my diverter valve is faulty?

What are the symptoms of a faulty diverter valve?
  1. Hot water taps that only reach luke warm. If your sink, bath or shower is not running hot, it could indicate that there is a problem with the diverter valve.
  2. The water only gets hot if the heating is on.
  3. The water is hot, but the heating fails to come on.

Makhlouf Kindl


How do you know if your boiler is overheating?

A build-up of limescale, sludge and other debris in the central heating system can be detected before the boiler will begin to overheat. If you've noticed that any strange sounds from your central heating system or that any radiators haven't been heating up properly, then they're strong indications of a blockage.

Osvaldo Stroud


Why does my boiler fire up then cut out?

If your boiler's pump is faulty, then it can cause your boiler to switch off. As a pump is used to move water around the central heating system, if it is not working properly, then hot water could just stay in the boiler rather than be moved around the system. This can trigger your boiler to cut out.

Youseff Hofeman


How do I stop my boiler from overheating?

The most common causes of boilers overheating is limescale and sludge build up.

Preventing boiler lockouts from overheating is simple.
  1. Hot flush your boiler to remove limescale and heating sludge.
  2. Add central heating inhibitor to your heating system.
  3. Install a scale reducer.
  4. Install a magnetic system filter.

Senida Gravalos


What can go wrong with a boiler?

Intermittent or no heat and hot water can often be due to either broken diaphragms and airlocks, faulty motorised valves, a broken thermostat or low water levels. You can start by checking if the boiler problem is caused by fault of the boiler pressure or thermostat, as these are easily accessible.

Celerino Franck


How do you hot flush a boiler?

Flushing and Draining Techniques
  1. Turn off power to boiler, and let water cool until it's just warm.
  2. Turn off water supply valve, and attach length of garden hose to boiler drain.
  3. Open drain valve and air vents of all radiators.
  4. To refill system, close air vents on all radiators, and shut drain valve.

Leisy Grohskreutz


What happens when a boiler explodes?

A boiler explosion is a catastrophic failure of a boiler. There can be many different causes, such as failure of the safety valve, corrosion of critical parts of the boiler, or low water level. Corrosion along the edges of lap joints was a common cause of early boiler explosions.

Lindsey Osterhof


Why is my central heating too hot?

The reason that your water is either too hot is because the heating element is heating the water up, but not turning itself off, meaning there is a fault with the electrical element or maybe the central heating is too hot, causing the hot water to over heat.