Should I be concerned with this....and what is it?

[Speedbird1]

Hello. Attached is an image of one of the joints from underneath my Baxi Duo-Tec 33 boiler.
The system is 2 years old (it's had 2 annual services) and it was noticed on last service by the engineer who said he would return, drain the system and clean and tighten the joint.
I am now unable to get the engineer back for whatever reason so need to get a new one.
Is this potentially an issue or could it wait till next January service?
There was a sort of sticky, brown, thick goo on the valve which just wiped off with paper as it has in the past dropped off. (only once) so foolishly i cleaned it before photographing it,Doh!
Thank you for your time and any advice.

 

[Londoner2]

If i were you ill get another enginerr in to sort, looks like the joint has leaked over time and thats the build up which then dries and solidifies, it looks like sludge and other chemicals. On the plus side , weather is warming up you should be able to call any engineer out pretty quick.

It does needs draining, cleaning, refilling and tightening.

My new Eco Elite compact had a similar tiny leak, installer tightened but i can see a very tiny leak still but not band as yours. and i can live with it until next service as heating will niot be used much now.

 

[Speedbird1]

Thank you Londoner2