Ecomax 828e HW going cold after a few minutes

[lumoruk]

Recently installed a new secondary heat exchanger because it was going hot and cold, boiler would shut down due to over heat, this fixed that. After I installed it and turned it on it went to 83C+ and hot water squirted out of a pressure valve inside the boiler. then it stopped and didn't do it again.

Recently trying to have a bath it now goes cold after a few minutes. Heating on radiators is spot on.

symptoms on boiler;
temperature set is exceeded and widely off when turned high or low.
temperature at tap seems to follow what is set on boiler.
if I put tap to half way it stays hot
I have no problem with using the mixture shower, I presume due to the reduced hot water flow.
it sounds like the burner or fan not sure is going for those few minutes then turns off. but a flame is still shown on the control panel.
edit: oh okay I've got error s.53.

delay mode ~20 mins lack of water in system.

did that water escaping when I replaced the heat exchanger lose water from system? says 1.5bar on front.


I recently had a service I didn't have this problem before it I don't think, and it wasn't picked up in the service. I mentioned that a new gasket was required for servicing it. he said it depends on the results he gets from his tests, no new gasket was installed.

please help supposed to be selling my house with a working boiler.

 

[lumoruk]

Gosh, will reply to myself then. Replaced return flow sensor and cleaned up the cold flow sensor which had a sticky (greasy) limescale on it. Hot water ran for 12+ minutes without going cold

Had an email from Vaillant Technical too if it helps someone else;

"S53 happens when the difference between the flow and return NTC’s gets to 30° with both hot water and heating the boiler is designed for a differential between flow and return of 20°, S53 reduces the output to stop the boiler overheating, this can be seen on d40 (flow) and d41 (return)

D0 is for heating only not range rating the hot water, hot water cannot be range rated.

Things to try after replacing the DHX, the rubber hose on the flow pipe can become restricted feel very crunchy, if you follow the flow past the rubber hose it then “T”s off to the bypass under that “T” is a union which goes to the DHX if you undo that union there is a filter which protects the DHX. "