Blocked Plate Heat Exchanger? Why Your Combi Boiler Hot Water Goes Hot and Cold
Hot water going hot and cold can point to a blocked plate heat exchanger, especially on older or untreated systems. Here’s what causes it and why cleaning or replacement may help.
Blocked Plate Heat Exchanger – Why Your Hot Water Keeps Going Hot and Cold
If your combi boiler is firing up normally but the hot water starts hot, turns lukewarm, or keeps going hot and cold, a blocked plate heat exchanger could be the problem.
It’s a common boiler fault, particularly in older heating systems or systems where the water hasn’t been properly treated.
What Does a Plate Heat Exchanger Do?
Inside a combi boiler, the plate heat exchanger transfers heat from the boiler’s primary heating water to the fresh mains water coming through your hot taps.
The two supplies never mix. Heat simply passes through a series of very thin metal plates.
Because the waterways are narrow, it doesn’t take much contamination to restrict the flow.
What Causes It to Block?
One of the biggest causes is sludge and magnetite from the central heating system.
Over time, corrosion inside radiators and pipework creates black iron-oxide deposits. If the system hasn’t been properly cleaned and protected with inhibitor, this debris can circulate through the boiler and eventually restrict the plate heat exchanger.
Scale can also contribute, particularly where water hardness is an issue.
Signs of a Blocked Plate Heat Exchanger
Typical symptoms include:
- Hot water going hot and cold
- Water starting hot and then becoming lukewarm
- Boiler temperature rising very quickly when a hot tap is opened
- Boiler firing and then shutting down repeatedly
- Heating working normally but poor hot-water performance
- Unusual temperature differences across the boiler pipework
Sometimes the boiler itself is blamed, when the real problem is simply poor circulation through the plate heat exchanger.
Can It Be Cleaned?
Sometimes.
A plate heat exchanger can often be removed and chemically cleaned to break down deposits inside it. Whether cleaning is worthwhile depends on its condition and how badly restricted it has become.
In some cases, replacement is the better and more reliable option.
But replacing the plate heat exchanger without considering why it became blocked can mean the same problem eventually comes back.
Prevention Is Better Than Repair
Your central heating water matters.
A correctly maintained system should contain inhibitor to reduce corrosion, and heavily contaminated systems may need cleaning before fresh inhibitor is added.
A magnetic system filter can also help capture circulating magnetite before it reaches vulnerable components inside the boiler.
Regular boiler servicing is therefore about more than checking whether the boiler fires up. The condition of the heating system connected to it matters too.
Hot Water Problems in Brighton & Hove?
If your combi boiler is producing lukewarm water, fluctuating temperatures or constantly firing and shutting down, don’t automatically assume you need a new boiler.
The fault may be repairable.
Dales Boiler Services provides boiler fault finding, repairs and servicing throughout Brighton, Hove and the surrounding areas.
Experienced local boiler engineer. Straightforward diagnosis. Repair where practical.
Dales Boiler Services
Boiler Repairs • Servicing • Installations Brighton & Hove
