Radiators warm at the top but cold at the bottom <PigletJohn klaxon!>

[AnnOnymity]

Is this likely to be sludge and is a powerflush likely to solve the problem? We're in a very old house with (probably) very old pipework. There are 14 radiators, two different types (see pictures). Or should we be thinking about replacing the worst affected ones with something new?

Not sure if it is relevant but the boiler is fairly new (3 years old?).

Have you bled the radiators?

No but I thought that was for the opposite problem (cold top/hot bottom)?

Good point!

that is indeed sludge. Also looks to me that you may have the small 8mm pipes, same as we do, in which case a powerflush won't work. (laws of physics).

suggestions:

• drain system, take off the radiators affected. Take outside and then flush out with a hose. BUT they may be so sludged/rusty that replacement would be well worthwhile.
• then, once you have physically removed as much as possible, use a chemical cleaner, one for older systems.
• fit a magnaclean and empty it fortnightly to start.

been there!

Powerflush made very little difference in my house (1890, radiators and pipes probably installed in the 1970s).

In the end the lot was replaced during building works. We got Jaga radiators, which are a marvel. More efficient and we found, a lot cheaper to run than the conventional kind.

We have similar problems... Have had radiators power flushed and that helped, but it's still not perfect. We have an old house too and while the boiler's new some of the pipework must be pretty ancient.

What works for us is to go round the house when the heating's on , turning off all the radiators that are properly hot (or all except one or two if none of them are working properly). You can then hear the water gurgling its way through the pipes which seems to clear the system. We had to do this when we first put the heating on this autumn but it's been fine since then.

This is all really helpful, thank you.

I'd never thought about the pipes before, but having had a cursory look I can see that they're all different (but small), and the coldest radiator has the narrowest pipes in and out of it.

hot at the top, cold at the bottom is insufficient flow. Turn off all the hot ones. Does it now heat up?

Hot at the sides, cold in the middle is sludge.

If the radiator pipes are the size of a pencil, power flushing may not work.

Does your boiler have a pressure gauge (probably not) or a feed and expansion tank in the loft, like an old WC cistern?

We have possibly Britain's most complex domestic boiler system. We've only been in the house for a few months and still aren't sure how it really works (understatement of the year).

I've added some pictures.

We have two identical boilers and two hot water tanks, but only use one of each as our first gas bill after using both was eyewateringly expensive. We also have switches that can change it over to oil should we wish to (which we don't). The system was designed by the previous owner who was obsessed with never running out of hot water.

The hot water tanks are next to the boilers. Both are downstairs in the utility room. The cold water feed is in a loft above the bedroom above this utility room.

I can't see a pressure gauge anywhere.

Will answer the Qs about which bit of the radiators exactly are hot/cold when they come on later.

when you say tanks, I think you mean hot water cylinders. What colour are they?

Are there any water tanks in the loft? What size?

I see you have Viessmann boilers, probably Vitodens 200, so you have an expensive and probably high-quality installation. Look at the top right corner of the front of the casing. I imagine you have a large house or small hotel with several bathrooms.

Go to the Viessmann website and look at the list of Approved Installers in your area. Probably one of them put it in, and the same or another has been maintaining it, and will be able to see how it is designed.

Your boiler room probably gets very hot as the pipes are uninsulated. Get some Climaflex or similar. They are probably 22mm diameter.

BTW I can see the temperature knob on one of the boilers is set to max, which will be about 80C. If you turn it to point at the round blob, that will be about 60C which is the most efficient temperature. If your radiators are undersized you might have to turn it up in very cold weather.

The black funnel-shaped thing is a Fernox TF1 system filter which traps circulating sediment particles. You ought to squirt out the sediment, do it today and then once a week until it stays clean; then once a month, then once a year. It doers not need a plumber.

You can probably download, or request, the instructions here

the lower row of pictures

instructions

Ooh! We had an elderly Viessmann boiler in our house in France - it was huge and lived in the basement. It had been the very first Viessmann in the village and everyone had been so impressed with it that several more were then installed in the area. An elderly plumber in the next village knew them all well and had painstakingly maintained them for decades - they were very complicated and very highly thought of. Quality stuff!

Yes, by tanks I do mean cylinders.

Yes, it is large house. Georgian 5 beds, 3 bathrooms plus 2 toilets.

So do you think that squirting out sediment from the funnel thing will help with the radiator problem, or is it just something we should be doing to keep the boiler working well?

Don't know about the size of the water tank in the loft. I'll need to get ladders out and look.

Thank you so much for all the advice. I am so in awe of your knowledge and the amazing advice you give on MN.

P.S. A few weeks ago you gave me great advice on painting exposed plastered walls which I followed to the letter and that worked out very well too.

squirting out the captured particles will prevent them settling into more sediment.

When you have found out about the loft tanks (look for one 18"x12"x12" with a ballcock inside) we will decide if you can clean it yourself.

Your boilers will have had at least a 5-year warranty, and probably ten years on the heat exchangers, so arrange an annual service. That might be an installers details on the sticky label I can see. If you can find the serial number, you can ask Viessmann when the warranty runs out.

Right, I've been up in the loft to have a look. I couldn't get a decent picture as the light was too dim but have drawn one! I think it is the size you suggested. I couldn't get close enough to look for a ballcock but assume there is one.

I also felt the radiators carefully last night. They are mostly hot in the top 3rd and at the side with the valve that isn't the the valve that adjusts the temperature (hope that makes sense).

Boiler is a Vitodens 100-W.

Ok

It seems you have open-vented Vitodens 100 which is relatively simple and you can give it a chemical clean, if you want.

You are going to have to get closer to that F&E tank. You are going to have to tie up the ball-cock float and bale out the mud and dirty water into a bucket, and sponge it clean, then draw a bucket or two of water out of the drain cock (there may be one near the boiler), then tip in the cleaning chemical, then untie the float so it fills up again. Do you think you can do that? Otherwise a plumber or competent handywoman can do it.

In a few weeks, after the chemical has worked, you do something similar to drain out the chemical and loosened sediment. While it is working, I recommend cleaning out the filter every day. The amount of sludge you get out should reduce as the system gets cleaner.

I am in awe. Piglet John you are fantastic.

I still think PigletJohn is female, like a WonderWoman type character,

Will he/she ever reveal themselves

P.s.

For an experiment, turn off your hottest radiators and see if the cool ones warm up. If only some if them do, turn those off and see if the others get hot. If they do, with no cold patches, you do not have a bad sediment problem so will not have to do all that.

Look for sticky labels, or tie-on tags, with the name of any corrosion inhibitor and date used. Most common brands are Sentinel or Fernox.

Thank you so much. I really appreciate the time and thought you have given to this. I'll let you know how I get on.