3rd Gen Thermostat, DHW runs cold due to boiler modulation dropping down to 8%

[Connell]

Hello to all

I have recently had a Viessmann 100-W 30 combi installed with no hot tank. The 3rd Gen thermostat was also installed and setup in November 2021, all appeared to be working correctly.

Today I found the hot water initially running hot and gradually cooling down to tepid, I viewed the diagnostics on the Vicare application and could see the burner modulation dropping slowly down to 8% and remaining there.  This was not enough to heat the flow of cold water.

The central heating was functioning correctly as far as I could see Modulation 45-65% and the water temp observed whilst the CH was running raised to the set 60 degrees. But again cooled when the hot water was run from the tap, Modulation again down to 8%.

There are no error codes observed on either the thermostat or the boiler.

I have reset the Thermostat and the Heat link twice to clear any learned information but this has not cleared the issue.

Please advise if this has been observed else where and if it could be isolated to either boiler or thermostat.

I am also contacting the installation company and Viessmann support for guidance/assistance.

Many thanks in advance 

Connell

[Connell · Accepted solution]

Hi Christian, thank you for your response I believe you are correct, I did substitute the Nest with an EPH-CP4 which did not resolve the issue.

The issue had occurred over the weekend and was reported to the installation group, they arranged a warranty visit which I am pleased to say occurred the following Tuesday.

An engineer arrived from Viessmann and quickly cleared some debris from the DHW flow sensor and fitted an inline filter to prevent it reoccurring.

Regards

Connell

[CristianC]

Hi there. Thanks for reaching out. On combi boilers the thermostat does not control the hot water. I suggest you get in touch with your boiler manufacturer for more details. Let me know how it goes. 

[Connell · Accepted solution]

Hi Christian, thank you for your response I believe you are correct, I did substitute the Nest with an EPH-CP4 which did not resolve the issue.

The issue had occurred over the weekend and was reported to the installation group, they arranged a warranty visit which I am pleased to say occurred the following Tuesday.

An engineer arrived from Viessmann and quickly cleared some debris from the DHW flow sensor and fitted an inline filter to prevent it reoccurring.

Regards

Connell

[AlexD]

That is great to hear @Connell . If anything else comes up that me or any of my colleagues can try and assist with, make sure to let us know. 

[DragosC]

Hi there. I'm just following up on our last message. Do you still need our help? Keep us posted. 

[AlexD · Accepted solution]

Hey there, I haven't heard from you in a while so I'll be locking this thread. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the community. Thanks, AlexD.