RAVENHEAT - possible airlock? What could be root cause? Help diagnosing please.

[Magslowe]

Hi, I'm a landlady and my tenant is worried his Ravenheat combi-boiler will explode because it made strange noises, then steam shot out and water came running down the wall.
This same thing happened back in March - so it's happened twice in 5 months. A gas safety registered engineer visited on Tuesday this week and said the pressure is fine after turning it off and on again and it ran normally during a 30 minute test. He therefore couldn't find anything obvious to repair and just said to use it as normal. He suspects an airlock on both occasions. I'm feeling worried though.... Can the boiler explode due to an airlock if a part inside the boiler is faulty? What are the likely causes of an airlock happening? Is this a rare problem in combi-boilers - never heard of it before!? Should I get a second opinion from another gas engineer?

Further info:

• The hot water is set to maximum temperature, yet it's not very hot when coming out of the kitchen tap. Could this point to the root of the problem?
• The gas engineer mentioned the diverter may be faulty but he wouldn't be able to tell just by examining it and doesn't want to replace parts without being sure they're at fault, due to the cost to me. I'm happy about that but nervous that we've not got to the root of the problem.
• The gas engineer did notice that the pipe that sticks outside, which I understand lets water out when the pressure is too much, isn't the correct width - should be 15mm (or was it 12mm?) but it was less than that. Any comments about the risks of this pipe not being the correct width gratefully received i.e. should I get it replaced asap by a gas engineer because it's very risky or is the risk minor? What might happen?

Thanks for your help!

 

[lame plumber]

its probably a well known problem that a decent technician can id, however being its a ravenheat they are renown for leaking like sieves and any work on them normally causes more leaks as does over pressurising them due to your fault, but they fail safe and the water leaks down the outside wall as you said. If its an old one consider a new boiler or just get it repaired but expect leaks idc. omho of the ravenheat

apologies for not telling you the probable causes but your not gsr and therefore this site wont provide an answer as such.