Vokera Syntesi 29e - Hot water runs cold

[Jim1758]

Hi guys,

A Vokera Syntesi 29e has a problem with the burner cutting out every minute for about 10 seconds, hence the water runs cold briefly. No errors on panel and pressure is fine. Could it be the domestic heat exchanger blocked? Any suggestions appreciated, thanks.

 

[kevplumb]

sounds promising

 

[Agile]

It could well be but it can be other things as well. There may be a non return valve which has jammed.

The way to see if its blocked is to measure the temperature differential across the plate HE. It should only be about 15-20° ! If its much more then its going to be blocked or the pump is blocked/failing.

If you cannot measure the temperature then the flow and return should both be too hot to touch. If the return is easy to touch then its blocked.

Tony

 

[Jim1758]

Thanks for the advice. Fitted a new non-return valve under the bath and the shower / boiler has worked faultless for about a week. However for the last two days it has started doing the hot and cold cycle when showering, again!

 

[scatmanjohn]

Its almost certain that it is what you think it is.

Just as it cuts out, turn off the hot tap and watch the display on the boiler.

If it changes to about 90 deg you need a new DHW HEX.

Measures need to be taken to stop it happening again, powerflush if req'd or matbe just a magnaclean fitting.

 

[Junkyardjunior]

The 2 most common causes for hot and cold water from a syntesi are partially blocked venturi and minimum gas pressure to high. A service will sort both of these problems

 

[Jim1758]

Thanks for the replies so quickly. I should have said that the boiler was serviced two weeks ago as soon as the problems started and also the pipe to the expansion vessel was fairly clogged (which cured a pressure problem). It seems that all the problems seem related to build-up in the system. The whole system is only three years old and inhibitor was put in when fitted. Sounds like a magnaclean is worth investing in!

 

[Jim1758]

Hi all, just to close this topic off for anyone else with a similar problem. It was the secondary heat exchanger (DHW) that was blocked - a new one cured it. I have added a Magnaclean 22mm to protect the system in the future. Job done!