CH advice please.

If you're getting clogging every year on 50mm pipes, that suggests a substantial amount of corrosion. Are they cast iron rather than copper? Do you have inhibitor in there?

Just an off the wall thought, but I wonder if it would be feasible to drain the pipes and push new plastic pipework through the middle of them? They did that when replacing our cast iron gas pipes with plastic: they redid the whole street with essentially no internal changes, just a meter change.

It might need some digging out of bends and T junctions that aren't accessible, but might be less disruptive than re-plumbing, assuming a boiler replacement is inevitable at some point.

Theo

When I read your post, the same solution occurred to me before I read Theo's reply.

What is the pipe layout of your system, and does it equate to any of the standard Honeywell 'plans'?

Assuming that it's a pumped system, you really need smaller pipes. With

Thanks for the reply, Roger, The system is 80 years old, the boiler is 40 years old. There is one pipe which goes up from the boiler to the the loft, then down via 4 drops to the rads, 2 per drop. There are cavity walls either side of the central stair well, and the drops are inside the cavities, two each side.

My real question is : is it true that a modern boiler will not work with this installation?

Yes, the pipes are iron.

The drops (see my reply to Roger) are inside cavity walls, so not accessible.

I really want to replace the boiler without disrupting the pipework

Assuming the basic layout is the same with feed and return pipes and the rads arranged in parallel between them, I can't immediately see any reason why a modern boiler could not work with the system - unless there is a material incompatibility with that much ferrous metal in the system. Even that seems unlikely given most modern rads are steel anyway. You would need a decent filter on the return though to protect the narrow water pathways in a modern HX.

TBH, even if there was a reason to not do it, you could sidestep the issue with the addition of a thermal store - modern boiler heating that indirectly, and it heating the rads with its own pump.

I expect this is more a case of it being unfamiliar for the fitter and perhaps a bit of hassle transitioning to the existing pipes from modern sizes of copper.

Very likely. It sounds as if your radiators are in series whereas systems installed in the last half century have invariably had them connected in parallel, with one end of each rad connected to the flow pipe and the other end to the return pipe.

How does the spent water get back to the boiler - there must be a return somewhere, from the end of the run?

How about getting rid of the big pipe in the loft, and installing 2 new pipes - a flow and a return. Then connect the two drop pipes to each rad, one to the flow and the other to the return. You could use 15 or

Eventually all the dissolved oxygen will dissapate so the inside of the pipes will not create any more black gunge, but if you drain the water out and refill with fresh water then you start the sequence again, unless a LOT of Fernox is added.

How may KwHs of gas to you use every year, out of interest ?

About 800-900 gas units, times 40?

There are 4 drops (in parallel) each with 2 rads in series.

The 4 drops combine under the floor, returning to the boiler as a single pipe.

None of the pipework after the loft is accessible without tearing the house apart :-)

Thanks for all the replies so far.

I could get a few more years out of the boiler if the pipes were a bit cleaner. Is there any good reason why a power flush shouldn't be used?

I would imagine that it involves pumping stuff around the system. With wide-bore pipes the flow velocity might be too slow to dislodge or carry sediment around the system as the pump will be designed for 15/22mm piped systems.

Tim

Cubic metres? 900 = 10,226 kWhr

Tim

But the radiators would be the issue here I think. It might be time to bite the bullet and get a more modern system. I seem to recall those older systems did use cast iron pipes, like slightly smaller versions of what we used to see in schools and the like. If it is, maybe they would have a significant scrap value? Brian

but with an Imperial meter it's x30-ish so c.25,000 kWh

Is the top of the cavity wall accessible from the loft? Is the cavity filled? (you said hallway walls, so I suppose not if it's internal?)

It might be possible to fish new pipes through the cavity with relatively small holes, roughly the size of an electrical socket. Somebody would drill a hole at the bottom of the drop, and the drop a new pipe down from the loft and pull it through the hole. The hole would then be filled - either with the piece removed, suitably modified, or with a new plug. There would be some making good of the surface finish, but not massive disturbance. You could also use plates like these:

If you were to do this I'd install feed and return pipes for each rad, so you're on a modern system. Then all the plumbing junctions are accessible in the loft. Ideally I'd do it in 15mm as that allows a more efficient low temperature system than 10mm microbore, if the radiators were going to be replaced at any point.

Theo

It would be worth asking the powderflush people what they reckon about 50mm pipes. It may be, for example, that the surface behaviour of the abrasive they use isn't as effective - eg because the granules are too small to effectively scour a wide pipe, as the path of least resistance in the middle of the pipe is wider.

I'd imagine you could do a liquid power flush with a big enough pump, but it might not be a piece of kit heating engineers typically have.

On that note, OP, is there a separate pump in your system, or are you relying on a pump in the boiler? If the latter, you'd need to install a separate pump suitable for 50mm, which is a bit out of the traditional comfort zone, but I assume they aren't uncommon on industrial systems.

Theo

With 2” pipes I was assuming no pump at all…

Tim

You can help things by thumping all the pipes and rads with a rubber hammer (or you can get pads to go on the end of an SDS for the purpose). The vibration will shift more crud.

Reversing the direction for a second go also helps.