Takagi TK3 hot water not working

I had Takagi tk3 installed for both radiant floor heat and domestic hot water. We have two bathrooms and the radiant system is installed in about 1/2 the downstairs floor area. At first the hot water worked fine, now it only works when the radiant floor thermostat is turned up so it clicks. There is a remote installed which shows no error codes. The hot water comes out of the tap only when the remote shows a steady red light, the fan starts, and the gpm outflow shows a higher output-- 2.7 gpm or so. I cleaned the water filter and have an Easy Water descaling device installed. When running just hot watsr in the tub with the remote set at 130 I notice an intermittant temperature and flow rate from the tap. Do i just take the front cover off to check for dust etc?? How do i clean the flame sensor and burners. The hot water does work, i just have to bump up the radiant heat thermostat to do it. Not good for energy or water savings right now

Why not call the installer you said this is a fairly new installation?

Takagi has a flow sensor that triggers it to fire up.
The burners are not something you want to try and adjust it sounds like a flow rate problem not telling the Takagi to fire.
Domestic water should have priority over the heating system.
Post pictures of the piping and valves etc.

One thing you could check is the inlet water filter on the bottom of Takagi cold water inlet, its a black cap you unscrew it and clean the screen of any debris.

Turn water off before you unscrew that cap and lift the handle on your relief valve to release pressure in the system first and use a bucket to catch the water that will leak out.