Water crossing from HW to CH

[Bob49]

Hello,

I have an issue where the resting pressure on my boiler is rising slowly over a number of days. I then have to drain some water out of a radiator to get the pressure back down. I have removed the filling loop but this did not solve the issue. So I reckon the plate heat exchanger is pinholed.

But are there any other ways water can cross from the HW side to the CH side?

I was thinking maybe the diverter valve, but I don't fully understand how that works.

So my question is can a diverter valve (faulty or not) allow a little water to cross from HW to CH or vice versa?


Thanks

 

[Mike13]

Do you need to bleed the radiators regularly? if so it could be corrosion.

 

[Bob49]

Do you need to bleed the radiators regularly? if so it could be corrosion.

Thanks Mike, not really, there is sometimes a small amount of air in the towel rail, but that's it.

What could be corroding and how does that increase the pressure?

 

[kidgreen61]

Had this last week, 15yr old WB 28i junior.
Plate heat exchanger was passing mains water into heating side.
New plate sorted it.
You can test by isolating cold inlet to boiler, if pressure doesn't increase, you've found your problem.

 

[Mike13]

Rust in a rad converts to haematite and gives off hydrogen, which increases the volume in the radiators, so the pressure has to rise. If you let it out in a fairly dark room and light the gas coming out it will be a dim blue flame.