When to change a radiator?

[milleniumaire]

As part of a loft extension 16 years ago a couple of 600mm high x 700mm wide radiators were installed. As a result of poor flow rates in the loft these radiators no longer warm up and I'm in the process of flushing through the pipes, which has so far removed a lot of sludge. The radiators themselves have also been removed and flushed through and again there was a lot of sludge in them. See my other posts for details if required.

For some reason, the lockshield valves are connected to the radiator using 3/4 inch(?) connections, whereas the TRV's are connected using 15mm connections. I've had to remove the valves to enable me to flush the pipes so plan putting on new valves and will use 15mm for both.

Although the radiators have been flushed outside, I'm wondering if I should take this opportunity to replace them. Googling suggests radiators should be replaced every 15 to 20 years, so on that basis it would seem to be the right time, although the radiators in the rest of the house have been in since the house was built 21 years ago (apart from a couple that had to be changed). Visibly, there's nothing wrong with the outside of the radiators and I would be getting replacements that looked similar and minimised the hassle of fitting i.e. the same size.

I've read that other reasons for changing radiators is because modern radiators perform better! The existing radiators appear to look very similar to modern radiators so not sure how that would be the case. I don't know what brand the existing radiators are, but they are Type 11's (1 panel with fins).

My current motivation for possibly changing these radiators is because they are disconnected, I'm changing the valves anyway and there is a lot of sludge in the loft pipes, so I'm assuming this has come from these loft radiators, but I'm not sure as it could have found its way around the system and settled in the loft pipes due to the poor flow.

So, would there be any benefit in changing these two 16 year old radiators? Are "modern" radiators really that much better?

PS. The last radiator I changed due to a seized bleed valve was replaced by a Quinn round top radiator, which used less water, although I do worry that the reduction in the internal volume of the radiator may also allow it to sludge up more easily. Quinn appear to have gone out of business, so are no longer available.

 

[Chuck]

My rule of thumb is that when the first radiator starts leaking, replace it. When the second one starts leaking replace the whole lot.

The laws of physics haven't change in the last 16 years and any improvements to the design of radiators since then won't be enough to justify the replacement of an otherwise okay radiator.

The radiators in my own house are about 30 years old, single and double panels (nothing special), and are still fine. I converted the CH from open vented to sealed about three years ago, cleaned, flushed and added Fernox and have had about one tablespoon of magnetite collected in the magnetic filter in total since then. I suspect that the radiators will outlast me now.

If you haven't done so already, I'd recommend considering converting from open vented to sealed CH. Pretty much stops corrosion in its tracks. Also, if you ever do have a leak it limits the damage and alerts you to the problem immediately.

 

[milleniumaire]

Hi Chuck, thanks for responding. Our CH system is sealed and always has been as the house is 21 years old and we've owned it from new.

It does seem pointless replacing radiators for "modern" versions that look the same, but then I've no idea what's happening inside the radiators!

 

[SimonG]

I wouldn't change them unless you have a problem with them.

 

[Ric2013]

I was reading some manufacturer literature about the 'efficiency' of the newest design of radiator. Efficiency was defined as heat transfer per kg of steel used in the manufacture. In that case, keeping your old radiators wins hands down.

My heating was installed in 1989, I think. I've owned the house 12 years and not had a single radiator fail.

In terms of energy efficiency, a more 'efficient' radiator may be one with a lower water content in that this limits the chances of the room temperature overshooting the design temperature (more likely in a timber-frame room than a brick one), but the converse argument could be put forward that a high water content is desirable so that the panel remains warm for longer after the heating switches off meaning that the boiler spends less time cycling on and off.

If you have a condensing boiler, then it may be better to have radiators sized to allow the boiler to run them at relatively low temperatures (the boiler runs more efficiently) , but there is nothing to exclude these radiators being 50 year old single panel unfinned type, so long as the outputs are correct. Willing to be proven wrong in this opinion, but yet to see a good enough explanation.

More to the point is, why is your heating system corroding so badly?

 

[oz-plumber]

I've found, over the years, that on larger systems the panels furthest away from the boiler seem to have a build up of sludge problem more so than panels close to the boiler.
All I can put it down to is the velocity / speed of the water flowing through the panel.

It could be a balancing issue that takes a few years to show, a pump issue or a pipe sizing issue.

If the system has worked fine for the previous years, just replace the radiators - they are relatively cheap.

 

[milleniumaire]

I wouldn't change them unless you have a problem with them.

I decided not to change the radiators and have now refitted one of them after giving it and the pipes a good flush through with mains pressure water. I did replace the 3/4" lockshield valve with a 1/2" valve. I had already changed the TRV last year, so the valves now match (both Drayton). This radiator It is now heating up nicely so I will move onto the next.

I've found, over the years, that on larger systems the panels furthest away from the boiler seem to have a build up of sludge problem more so than panels close to the boiler.
All I can put it down to is the velocity / speed of the water flowing through the panel.

It could be a balancing issue that takes a few years to show, a pump issue or a pipe sizing issue.

If the system has worked fine for the previous years, just replace the radiators - they are relatively cheap.

It does feel like this is a flow issue. They are the furthest from the boiler and the highest in the house! These loft radiators have been okay for around 15 years and it is only the last couple of years the issue has appeared. 5 years ago we had some UFH installed as part of a kitchen extension, I did wonder if this had an effect on it. I also wondered if the 8 year old pump in the boiler might be losing some of its "umph"!

I plan to replace the 15mm supply and return pipes upto the loft with 22mm pipes at some time, but first I want to get the loft pipes and radiators flushed through and working and so far so good.