Combi-boiler pressure keeps rising when cold

[TedTrippin]

Hi,

I have a Worcester Bosch combi boiler. I'll update the thread with model when I get home. It's like the 24i except it has 2 dials for CH temp and HW temp.

I noticed the pressure gauge was in the red. I went to check one of the rads which usually gets air. No air. I drained one of the rads to get the pressure down to 1.5. Before I went to bed the pressure was back up to 2. This morning it was about 2.5. I haven't been messing with the boiler and I haven't added more water in some months.

Before I call out the plumber is there anything I can check to diagnose the issue?

 

[John D v2.0]

filling loop letting by (£10s fix) or hot water heat exchanger leaking (£hundreds)

1 Make sure the filling loop is actually turned off on both taps, and unscrew the flexible hose (turn off the stopcock first if you're worried) Then you'll see if it's letting by.
if not and it still increases, 2. For the dhw exchanger, turn off the cold water supply before the heat exchanger (boiler inlet) and see if it stops increasing. Open a hot tap and see if it drops slowly.
Others may have quicker ideas to check.

 

[muggles]

Is your filling loop letting by? If not then your plate heat exchanger is probably knackered

 

[TedTrippin]

Cheers for those ideas. Will have a go when I get home.

Hope I can disconnect the filling loop, its one those "hard" ones that you need to stick the plastic key in.

 

[dilalio]

Hope I can disconnect the filling loop, its one those "hard" ones that you need to stick the plastic key in.

Then you can't! Turn off the main stopcock overnight and see if the pressure remains at set level... If it does then boiler needs a new internal filling loop or see if you can make this obsolete and fit an external filling loop.

 

[Madrab]

Turn off the main stopcock overnight and see if the pressure remains at set level

If you turn the mains off then it's going to stay at the set level regardless of what's passing, given the boilers mains inlet serves both the loop and the PHE

OP, time to get someone in methinks

 

[dilalio]

If you turn the mains off then it's going to stay at the set level regardless of what's passing, given the boilers mains inlet serves both the loop and the PHE

Just testing

 

[John D v2.0]

If you turn the mains off then it's going to stay at the set level regardless of what's passing, given the boilers mains inlet serves both the loop and the PHE

True but If he leaves a tap open overnight, the pressure will drop off it's the dhw exchanger, If it's the loop it will stay the same

 

[phredda1]

If the key isn't in the filling loop how can it increase the pressure?

 

[ollski]

If this is the cdi 24/28 then it's usually the plates hx pinholed

 

[TedTrippin]

I've been googling, it looks similar to the 27cdi. Can't find the model number on the thing!!

Anyway, I closed the main inlet and opened a hot water tap. The pressure went down. So guessing that's the heat exchanger done in.

I've got a plumber coming tomorrow save me breaking anything.

 

[John D v2.0]

Good diagnostics, do let us know the final outcome!

 

[dilalio]

So guessing that's the heat exchanger done in.

Yep. Sounds like that's the culprit.

 

[TedTrippin]

Yep, was the heat exchanger. Decided to get the plumber out instead of trying to fix myself. Turns out I have a Greenstar 30 si which looked way more fiddly than the CDi's I was youtubing.