Combi boiler - Hot water runs hot then cold

[Chancer]

Hi All.

I have an Ariston Microgenus HE 24 MFFi which has recently developed 2 problems.
First, the water is not hot enough - around 45°C or so. Secondly, when you run the shower (thermostatic) or bath the water goes cold after about 8 minutes, and then warms up again. This repeats with shorter intervals.
There are no error codes displayed. The flow rate is 11 Ltr/min.
We have changed the secondary (plate) heat exchanger with no effect.

Any ideas?

Thanks in advance

 

[Sim77]

I would first make sure that it is not your thermostatic valve on the shower that is causing the problem

 

[stussy]

Is it the same problem at every outlet or just the shower?

 

[Sim77]

Faulty thermostatic shower will can mix hot and cold at all other outlets.

Off course this could be something else - but I would always start with checking thermostatic shower valves first as in my experience they fail way too often.

 

[Sim77]

... if thermostatic valve is fine next I would investigate DHW plate exchanger.

 

[IDCHAPPY]

Cough*no tech advice*cough
Are you gas safe registered?

 

[Sim77]

are we allowed to post advice regarding plumbing (how to check thermostatic valves?)

Thanks,

 

[kris]

Sounds like you defo have a fault with the boiler , unfortunately we cant give you advice on gas related problems, make sure your thermostat on boiler for the hot water is where it should be , and the pressure is ok ( if pressurissed ) probably best to contact your local engineer ,,,

 

[jtsplumbing]

More likely problem with shower, remember cold water inlet temperature will vary, and depending on temperature of incoming cold water this will affect the hot water temp, check temp of cold water in / to temp of hot out if you have a difference of about 35c then that's the best you can expect

 

[kris]

Thought he said it happens when shower or bath runs ?

 

[jtsplumbing]

Thought he said it happens when shower or bath runs ?

Sorry stand corrected, amount of people that complain about hot water temp from combi's in winter , more so with the smaller Kw ones

 

[IDCHAPPY]

Your right about that though JTS, the reason why i'll never fit under a 30 if there's a bath in the property :lol:

 

[townfanjon]

Possible cross flow going on here on