Ancient but reliable potterton diplomat 41/48 kettling

[rissole]

Hi,

I have a Potterton diplomat 41/48, with an indirect feed to the hot water system, and a separate pumped feed to radiators, currently not used.A fault on the header system allowed some air into the system, noticed as the boiler was kettling, and one pipe to the HW tank was hot, the other cold.

The header tank system is working again, and the gravity fed hot water system is circulating ie the return pipe is hot now, and we have hot water.The system is kettling for a little while before it turns off, and I'm assuming that there may be some scale in the boiler system, or that the gravity fed indirect hot water system has some air or scale in it preventing proper circulation.

Or do I just turn the thermostat down for summer? Do indirect systems usually have a bleed valve or are they arranged so air is pushed straight back out into the header tank as it fills? I would think they are...

I think there are some plates on the front of the boiler, I expect it is likely to be useful to drain the system, and remove these to try to remove scale in the boiler directly.? I have no manual or info for this model, but similar looking larger models have water chamber plates for this purpose in some pdf docs I found on the net.

Any suggestions gratefully received.
cheers
Rissole

 

[45yearsagasman]

Why bother with such an old fuel wasting boiler. If you insist on doing the work then the waterway covers can be removed (after draining) and boiler can be cleaned out. Replacing the rubber gaskets will be required and they may not be available. They can be made from suitable rubber sheet and cut to size. You have major problems however if the studs holding the covers are rusted and break during removal. I have done several like this but not for the last 20 years.

 

[bengasman]

As with any old open vent system, your system is probably heavily corroded. You need a pro to get rid of the limescale/magnetite.

 

[rissole]

Well, I've drained and flushed the system, and backflushed the lowest pipe runs back through the pump and boiler, and refilled with a system cleaner in there. I ran the system with the CH pump on for an hour or so, and then switched that off and left the HW system on for a couple of hours. The boiler is not kettling anymore..

I won't leave the cleaner in for too long, and will probably flush it all again today. I put some penetrating oil on the boiler plate nuts yesterday. Today, I'll see if I can shift them: but I wont try too hard: thanks to 45yearsagasman for the heads up on the danger of the studs snapping. The gasket will need to be remade as I can't find anyone stocking them anymore, so no point unless I can find some rubber sheet today.

Why haven't I replaced the boiler yet? The house is well insulated, running costs are pretty low, and the damn thing won't die! Payback period is around 10 years, if I can get a new boiler, and have it installed for around £1200. I can save more money if the kids just turn some lights and computers off. I'd rather go on holiday, etc. It is pretty ugly though.

I like fixing old things. I ride a 31 year old Yamaha XS850 in the summer, and drive a 22 year old Porsche 944 in the winter. A 54 year old boiler that was state of the art in the year I was born...

cheers
Rissole

 

[Agile]

Your old boiler is very inefficient perhaps 50% if you are lucky.

Its all very well calculating a "payback" time but that takes no accouint of the inevitable increase in gas and oil prices.

It may be fun riding an old motorcycle but there is no fun involved in continuing to use an outdated and inefficient boiler. Gravity hot water is also inefficient.

I would normally say dont open up the inspection plates on your boiler but in your case it might be a prompt for you to replace it when a few studs snap off.

Tony

 

[Nige F]

If it starts to kettle again - just stick some Fernox boiler silencer in the system save the studs and gaskets for the yam .

 

[Agile]

Dont encourage a luddite Nigel.

To improve the world we have to get rid of Gadaffi and Diplomats!