Radiator rust bubbles - start of problems?

Hello all, new to the forum, and being an electrical engineer I hope I can contribute in the future.

My first post however is asking for advice. We have two radiators on our central heating system that have developed bubbles in the paint finish. One is a normal radiator (lounge - Biasi P+) and the other is the kitchen towel rail (white painted finish).

The towel rail has bubbles where a few of the horizontal bars meet the uprights, these have a bit of rust staining however the metal underneath doesn't look to bad generally.

The lounge rad recently developed a bubble underneath on the back of a bottom 'fin'. Again, the metal doesn't appear particularly rusty underneath.

When the bubbles where first noticed, they were damp (and I think released some water when burst). Afterwards, they felt quite dry to the touch, but any leak could be slow enough to evaporate quickly?

They are not weeping considerably by any means, but there must be a leak to cause the bubbling right? I've also found we are topping up the boiler pressure (sealed system, combi boiler) once a week, maybe half a bar.

We are currently refurbishing the lounge, and when running some cables under the floors I took the opportunity to thoroughly check the pipe work. No signs of any leaks under the ground floor, and no damp patches to the ceilings either.

New Boiler and rads were fitted to existing pipe work approx 8 years ago. The system wasn't power flushed (didn't know any better at the time and it wasn't offered), it was treated with X100 however several room decorations later and topping up with mains probably means this is all but gone.

Questions:

1. Are the bubbles likely pin hole leaks?
2. Can these be repaired or is it safer to get a new rad (would be a shame, it looks pristine from the front)

The plan is to drain, fit new rads, mains flush a few times, run with X400 / X800 for a couple weeks, reflush and refill using X100.

Do you think this would be ok? I'd like to avoid the expense of a power flush if possible, the water is dark brown but doesn't seem sludgy.

Many thanks in advance,
Ian

If there was damp in the blister it sounds like pin holing. Two possible causes, duff radiators or bad corrosion in the system, perhaps due to a system design fault.

In theory rads can be repaired but just don’t go there, if one bit is pin holing you can bet there is more to come.

First get the system checked for pumping over or sucking in air, the most common causes of rusting in a system, apart from water leaks causing constant water changes, so that can be rectified while the system is drained.

Replace the rads and flush the system. If you don’t want to power flush take the rads off take them outside and put the garden hose through them. (factor in black sludge damage to at least one carpet while you are moving them )


footprints

If you are loosing half a bar each weak you have a problem somewhere.
Fresh water and it will rust radiators quickly. You have a leak somewhere.

As said if bubbles of water then its a leak. Will be made worse by cleaning chemicals!

If you are so mean that you do want to repair them then remove and drain the rad and then braze over the pinhole. Refit and sit back and wait for the next pin hole!

This does demonstrate just how important water treatment is.

Your water is brown! Don't you realise where the colour comes from?

Tony

Just twigged (brain was shutting down when I posted last night) as you have a sealed system it cannot pump over, and unlikely to be drawing in air so on the bright side that's a couple of faults eliminated

Best guess is leakage, maybe a tiny weep on lots of old valves if they were not changed when you upgraded the boiler, they can be too small to see but they all add up.

Ok thanks for the input all, I'll get the new rads ordered and fitted, flushed and treated.

I believe the slow leak is due to the failing rads and also the filling loop. On closer inspection it is damp from the non return valve part.

Rads don't fail unless there is a fault.

You need to identify the fault before you fit new rads!

Tony