Worcester combi boiler green star 25 si DHW issue

[Zehroni]

This boiler was installed in 2019 and was working perfectly until two weeks ago. I cleaned the central heating system and topped up the boiler. The boiler is in the upstairs bathroom, which is the highest point of the system. When there is a demand for DHW, the temperature goes to 99°C but the DHW is lukewarm. As soon as I switched on the central heating, all the heat inside the boiler transferred to the radiators, and the bathroom radiator — which is very close to the boiler — became very hot. Then the DHW started working again for two days and went back again to lukewarm. any idea? is it airlock in the system or something more serious? there is no error code

Also, how can I increase the pressure to more than 1 bar? The boiler has a keyless filling loop, and no matter how long I hold it open, it does not go above 1 bar.

 

[Zehroni]

Dear all,

I carried out further tests today and the central heating is working perfectly. I left it running for nearly an hour and purged the system to make sure there is no airlock. The DHW works as it should when set to 40°C. However, when the DHW temperature is set to the maximum 60°C, the boiler fires up, the water at the tap becomes hotter, and the boiler temperature rises quickly to 90–93°C. At that point the flame goes out, and the water at the tap gradually becomes less hot until it turns lukewarm. Then the cycle repeats itself.

Do you have any idea why this might be happening.

 

[CountryFan]

It could be a few things, it could be trapped air, but unlikely if the heating is working. If the system was dirty (you mentioned cleaning it) could have clogged the plate heat exchanger, if you live in a hard water area could have limescale restriction in the plate heat exchanger or a component maybe breaking down/broken. All of which (apart from trapped air) needs a gas safe registered engineer.

 

[Johntheo5]

This boiler was installed in 2019 and was working perfectly until two weeks ago. I cleaned the central heating system and topped up the boiler. The boiler is in the upstairs bathroom, which is the highest point of the system. When there is a demand for DHW, the temperature goes to 99°C but the DHW is lukewarm. As soon as I switched on the central heating, all the heat inside the boiler transferred to the radiators, and the bathroom radiator — which is very close to the boiler — became very hot. Then the DHW started working again for two days and went back again to lukewarm. any idea? is it airlock in the system or something more serious? there is no error code

Also, how can I increase the pressure to more than 1 bar? The boiler has a keyless filling loop, and no matter how long I hold it open, it does not go above 1 bar.

IF the expansion vessel prefill pressure is 1bar then the filling pressure should be 1.5bar. This filling loop is often supplied from the Mains inlet to the boiler for DHW, item 4, below, and will/should definitely be > 1.0bar even with the boiler upstairs. Can you post a photo of your filling loop and valves etc.

 

[CountryFan]

The pressure should be capable of going well above 1.0bar as this is normally taken from the

IF the expansion prefill pressure is 1bar then the filling pressure should be 1.5bar. This filling loop is often supplied from the Mains inlet to the boiler for DHW, item 4, below, and will/should definitely be > 1.0bar even with the boiler upstairs. Can you post a photo of your filling loop and valves etc.

Yeah, but only as good as the incoming mains pressure.

 

[dilalio]

Blocked phex

 

[Zehroni]

IF the expansion vessel prefill pressure is 1bar then the filling pressure should be 1.5bar. This filling loop is often supplied from the Mains inlet to the boiler for DHW, item 4, below, and will/should definitely be > 1.0bar even with the boiler upstairs. Can you post a photo of your filling loop and valves etc.

View attachment 422030

 

[Johntheo5]

That valve may be opened now as its almost vertical, try turning it a 1/4 turn clockwise to shut it, also check that the valve spindle is moving as you twist the handle. Your mains pressure may only be 1bar but if so you will only have a pretty poor flowrate from your shower or HW taps.