Worcester Bosch hot water problems

[johnmichaels]

Hello, I've found this community really helpful in the past so I hope someone can help us with a boiler problem we've been having.

We have a Worcester Bosch 28i Greenstar Junior combi - 10 years old.

A week ago we had a leaking radiator pipe fixed. This involved either a full/partial drain of the system (unsure).

Ever since then we've been having hot water problems.
Particularly after having the heating on for long periods, running hot water will do one of two things:
1 - Nothing, just cold water comes out. The boiler doesn't fire up and just makes a 'clicking' noise as if it's trying but doesn't fire up. I have a video of this in an album below.
2 - Hot water comes out, but the pressure goes really high (3 or 4 bar) and water is dumped from the pipe outside.

The below album has 2 videos, both showing the boiler firstly just making a clicking noise while cold water runs from the hot tap, the second shows it tentatively fire back into life (eventually) and doesn't sound healthy.
https://photos.app.goo.gl/vpG4iDfuYPPam5tY7

We have boiler cover and two different engineers have been out to look at this but haven't managed to replicate the problem during their short visit. The first also changed the diverter valve.

I'm at a loss what to do next. It's an intermittent problem, and I can't pin down the exact pattern to make it happen.

Edit: And this evening we've just had the heating on (no hot water) and it's over-pressuring, making banging/thuding noises and dumping water outside.

Any ideas??

Thank you!

 

[martyndc88]

I'd say you've got a blockage/poor circulation around the boiler. Looks like the boilers not kicking in untill it dissipates it's heat. Pressure issue is flat expansion vessle or blocked hose

Does hot water go hot/cold

 

[johnmichaels]

Thanks for your reply martyn.

It doesn't really go hot/cold, it either provides the hot water or doesn't. It occasionally gives a little hot water but then goes cold.

Could the boiler be overheating because it can't dissipate its heat and therefore decides it won't heat any hot water/radiators for a while as a safety mechanism?

Thanks

 

[martyndc88]

It's probably blocked and can't circulate around the plate.

 

[johnmichaels]

Thank you for your help, it turned out to be the pump.

It was replaced this morning and we've had a perfectly running boiler since.