Flushing Combi - Necessity

[Geoff Lane]

I've recently had an extension built with a new Glow Worm 30ci combi boiler fitted.

There is a little old pipework remaining and one small rad otherwise the system is new.

My previous gravity system gave no trouble, apart from the occasional pump, it worked faultlessly but owing to a need for instant hot water I went for a combi.

After 16 months the secondary heat exchanger failed, as I had not had the apparently mandatory service this was not covered by warranty so I had a very expensive repair.

The service engineer said this was due to the system not being flushed as the heat exchanger was blocked.

I am now led to believe that system flushing appears to be a necessary requirement for combis due to the design, how important is this flushing, I would have thought any modern boiler should have some filtering system to prevent fouling of the internals.

Geoff Lane

[Andrew Gabriel]

Which side blocked? If you are in a hard water area, you can expect the secondary side to scale up. I recently descalled a friend's one in Baxi 105, but that took 4 years to block, with a family of 5 including two babies.

There shouldn't be any new debris appearing in the heating circuit in the first place (at least not within 16 months).

[Doctor Drivel]

Sounds like crud in the primary side.

Desludging is needed in all systems not just combis. Also fit a Magaclean filter on the CH return, as this will catch debris and iron.

Depends on how much crud was already in the old system. The Glow Worms are good boilers, and a failure like this is very rare.

[Ed Sirett]

Complete cleaning of the existing pipes and radiators (by flushing or otherwise) is essential. It is best practice. It is required by many of manufacturers. The guarantee may depend upon it. It is frequently the most time consuming part of the job of replacing/upgrading a heating system. It is the activity that divides the best from the rest.

The 2ndary plate heatXs in combis are great filters for crud so it is all the more significant for such boilers.

[Geoff Lane]

I would have to agree that flushing could only benefit but how essential is it; as previously mentioned my old gravity system worked for years without any flushing.

The new combi failed within 16 months, I am not an engineer but would have thought filters should protect vulnerable parts of a boiler.

Geoff Lane

[Doctor Drivel]

Most makers do not put them on. A few do. Alpha have a cyclone filter.

[Ed Sirett]

The old system was probably full of crud but it didn't have a big effect on it's operation. There is no problem with combi boilers _if_ the system is cleaned out properly prior to fitting, other wise there can be trouble as you have found out.

Thorough flushing now together with cleaning/replacement of the 2ndary heatX should do the trick.

[Doctor Drivel]

An fit a filter on the return to the boiler, which should be the case with any system anyway.

[Geoff Lane]

Are these easy to fit.

Geoff Lane

[Doctor Drivel]