Main Combi 30 HE . . . hot water disappears

[TheSalad]

Hi we have had a Main Combi 30 HE for about 5 years now and suddenly we are experiencing loss of hot water in the two showers we have. Any adjustment to the shower thermostat or water flow seems to trip the hot water off. A reset of the combi seems to bring it back.

We are replacing one of the cartruidges in the shower bar mixer as we thought that was the problem initially and it hasn't felt quite right recently. But suspect something more sinister as we experience the issue in both showers and have lost hot water to the whole house on one occasion.

Any ideas anyone? Help gratefully received. Thanks.

 

[dcawkwell]

Since the showers require a fast delivery of hot water.
What happens at the bath tap if you run a bath?
Is there any fault code on the boiler?
Does the water return after a few minutes or has the boiler actually
locked out due to a fault?

 

[TheSalad]

Thanks. I just tried it on the bath. Ran the hot water on full, no problem . . . . . but then reduced it to a trickle and slowly the hot water disappeared . . . . . pushed it back up to full flow and no hot water at all, gone.

Went to the bathroom sink about 2mins later and ran the hot water on full . . . nice and hot!!

But then tried again on the bath, full flow and it disappeared again.

It's a mystery . . . .

No fault code observed.

 

[dcawkwell]

Thanks. I just tried it on the bath. Ran the hot water on full, no problem . . . . . but then reduced it to a trickle and slowly the hot water disappeared . . . . . pushed it back up to full flow and no hot water at all, gone.

Went to the bathroom sink about 2mins later and ran the hot water on full . . . nice and hot!!

But then tried again on the bath, full flow and it disappeared again.

It's a mystery . . . .

No fault code observed.

Partially blocked plate heat exchanger. The boiler is getting hot and shutting down when supplying hot water. The boiler then has chance to cool and then resumes hot water delivery. Remove plate heat exchanger from boiler and flush out. All should be well.

 

[TheSalad]

"Remove plate heat exchanger from boiler and flush out."

Is that a big job . . . for a plumber?

 

[dcawkwell]

"Remove plate heat exchanger from boiler and flush out."

Is that a big job . . . for a plumber?

It is regularly done.
Difficulty depends on the boiler and layout inside also the boiler location
on the wall and access available.
It can be easy or really awkward. Some boiler manufacturers are just
plain stupid with layout of the boilers.

 

[TheSalad]

Update . . . . . . heat plate exchanger clear, needs new diverter valve.