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Hot water in tank in loft - PigletJohn are you around?

(18 Posts)
AmericanPastoral Mon 02-Jan-17 11:23:56

Following on from a post of a couple of weeks ago regarding asking advice about powerflushing (having been advised by a young plumber that we needed one as our system was overheating). My husband has been up in the loft and taken pictures which are attached.

We have an old central heating system (probably 20+ years) and have noticed there is a small tank in the loft which is constantly filling up with hot water. It’s right next to the cold water tank in the loft. Hot water pours into the tank from a pipe positioned above it. There was a lot of steam coming out of the tank so we have now temporarily covered the tank. The water in the tank looks dirty brown so I think it’s from the central heating part of the system. Would anyone be able to explain why the tank could be filling up with hot water. It seems an awful waste of energy. From looking on forums I wonder if it is an expansion tank which for some reason is constantly being filled with hot water.

The radiators seem fine.

Slightlyperturbedowlagain Mon 02-Jan-17 11:30:41

Not an expert but my guess is that it is the overflow/expansion tank for your heating. Hot water takes up more space than cold so needs to overflow as the water in the system heats up. When it cools it will take in some more from somewhere (the mains supply in our house) to fill up the small gap left due to the smaller volume of cold water. Bit odd if it's filling a lot though. If it's over-heating is the thermostat working?
I would always get a second opinion on heating matters before getting expensive work done unless you have someone tried and trusted as (from experience) they are not always right.

AmericanPastoral Mon 02-Jan-17 11:35:15

Another picture of the tanks.

MrCreosote Mon 02-Jan-17 11:38:26

How old is your boiler?

PigletJohn Mon 02-Jan-17 11:45:45

you have a severe fault.

Almost certainly there is a blockage of sediment in the pipes.

The pump is attempting to circulate water round the radiators; it is obstructed by the blockage, and is being forced to escape up the vent pipe (provided for this purpose) where it falls into the feed and expansion tank.

The tank has a pipe in the bottom which runs to the radiator pipes, and normally keeps them topped up. In your case it is probably feeding onto the other side of the blockage.

This is severe because the water gushing in the loft is exposed to the air, and becomes oxygenated. Water plus oxygen causes the radiators to rust from the inside, which both makes the sediment worse, and will eventually cause the radiators to leak or split due to rust damage.

Call a heating engineer to fix it.

For today, find the CH circulation pump and turn it to its lowest speed.

AmericanPastoral Mon 02-Jan-17 12:23:38

Thanks very muchslightly and MrCresote. The boiler would be about 10 years old.

Thanks very much for your advice PigletJohn. So if the problem is sediment in the pipes the solution would probably be a powerflush? I guess the British Gas homecare we have probably wouldn't cover this. It's most likely been like this for years shock

PigletJohn Mon 02-Jan-17 12:37:35

no, BG will not cover it. Furthermore they will charge you a high price to clear it, and if they find out you have it, will become reluctant to do repairs which they will blame on corrosion.

As well as having the sediment cleared, I recommend having a system filter fitted at the same time, which will capture future circulating particles before they can accumulate into another blockage. Cleaning can never get it all out. A filter will add about £100 to the cost.

PigletJohn Mon 02-Jan-17 12:40:20


both your loft tanks should have close-fitting plastic lids, which you can find in a DIY shed or plumbers merchant (measure carefully). This will keep dirt and drowned wildlife out. The pipes and tanks should be insulated, especially if the house will ever be left unoccupied.

MrCreosote Mon 02-Jan-17 12:56:04

If you have some money set to one side, I would also look into getting a new, combi boiler. They come with a magnetic filter as standard these days. The central heating part is a closed system and no need for water tanks.
If not, a good system flush and some inhibitor to help prevent any further rusting of your radiators and, as piglet John has said, have a filter fitted.

specialsubject Mon 02-Jan-17 13:30:35

Combo boiler means no hot water in a power cut and doesn't suit everyone.

Op - as PJ says there is a severe blockage, seen this fault before. The blockage needs to be found not just squirted! You also risk a damp loft with all the condensation.

Filter is indeed a good idea, learn how to empty it yourself.

Good luck in finding a competent fixer.

Slightlyperturbedowlagain Mon 02-Jan-17 13:35:18

Our non-combi boiler doesn't work during power cuts either as the pumps are electric.

PigletJohn Mon 02-Jan-17 13:51:22

but when the regular boiler breaks down, you can still have hot water, heating the cylinder with its immersion heater(s)

So it is not an urgent catastrophe, like when a combi goes wrong (more often).

If you have a multifuel stove, you can get one that also heats the cylinder.

Slightlyperturbedowlagain Mon 02-Jan-17 15:19:05

Yes pigletJohn I would personally avoid combi boilers for that very reason.

AmericanPastoral Mon 02-Jan-17 23:33:36

Thanks very much PigletJohn MrCreosote and Slightly. Any recommendations for a good person to use in the London area??

Sweets101 Mon 02-Jan-17 23:36:19

These aren't the ones that can overflow and the hot water come through the ceiling are they?

superram Mon 02-Jan-17 23:40:13

Eddie from Chiswick heating has been used by a number of our friends.

PigletJohn Tue 03-Jan-17 00:13:26

It would theoretically be possible for a feed and expansion tank (the small one) to get so hot that it buckled, but that would need a very unusual combination of circumstances. They only hold a gallon or two and the water would not be hotter than a radiator.

old immersion heaters were capable of boiling the cylinder if the thermostat failed "on" which caused the accident you are thinking of, when it filled the loft tank with near-boiling water. Modern ones have an additional cut-out to turn them off (and stay off) if they overheat.

Gas boilers have had overheat cutouts for many years.

AmericanPastoral Wed 04-Jan-17 12:06:23

Thanks superram and PIgletJohn. I've got someone coming tomorrow so fingers crossed the problem hasn't got too bad.

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