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Discuss Has my hot water cylinder coil broke? in the Central Heating Forum area at PlumbersForums.net

Hi All,

On Thursday there was a water leake a few steets away from us And we had no water most of the day.

About 10 minutes before my neigbour said the water supply was back on I remember hearing a fair amount of activity from our airing cupboard. I took this as water/air moving through as the supply/pressure was recaps being restored (it was partially, then fully)

The leak was fixed and all seemed ok but in the evening I notice the hot water was not clean. It was brown tinged and although I am not sure I thought I could smell a chemical smell.

I continued to run hot water off until it was clear.

Unsure if the coil had split I turned off the demand for hot water and left for the plumber to see the following day. I had manually twisted the presure relief above the cyclinder, which let some flow down the tundish, and I then checked if the system needs refil through the filling loop (it did a little At least but it is hard to gauge how much)

Just before the plumber came we noted the downstairs overflow bhind the toilet cistern was dripping and had been for some time (It still is)

the plumber thought the coild was fine and the dirty hot water was due to the the water supply and pressure being restore to the hot water cyclinder i.e. 20 years debris and crud distrubed at the bottom of the cyclinder. The reason for the drip because the pressure relief valve has a fault (because Ive touched it) orig isnt seating correctly perhaps with debris (assumably as the mains cold migh not have been clear itself once restored. The central heating had been on a couple of times since a filled and boilder pressure seemed normal (another reason he doesn’t think it was the coi)

he left and gave me his phone number but advised to run a few hot water baths to clean things out, and to call him this week if the drip hasn’t stopped.

Over the last two days I have rup about 10 baths full baths. not hot water bath has been clear, but the following cold one (from the refill afterwards the water is clear.

Anyway 10 baths later the water still isnt clear (only the ones run directly after the hot one).

Ive been watching the pressure gauge on the boiler and this hasn’t seemed abnormal to me i.e 1.5-2 bar when hot, 1-1.5 bar when cold, I have refilled using the filling loop throughout

I cant say I have left the cyclinder cold and then seen if several hours later it has gone dirty, I will try that next

Is this sounding like the coil, or just distribution of the dirt/silt at the base fo the tank. I cant figure out if it is the hot water cyclinder is clearing, or the dirty water from the central heating system is slowly being diluted and cleared from the hot water cyclinder! To me I’m thinking cyclinder because after running a dirty bath off from the cyclinder the next one straight away is clear and hasn’t had time to take get dirty from the water from the split coil.

Any thoughts or help would be very much appreciated.


Staff member
S. Mod
Gas Engineer
Normal as the water board doesn’t flush the lines out after work has been done always best to run a cold tap for around 10-15mins afterwards

you would be the other way round eg clean water going into the heating system as the unvented is a higher pressure than the heating system


Gas Engineer
also pressure would increase in the boiler as stated above the pressure in the cylinder is greater than the system pressure
you would be the other way round eg clean water going into the heating system as the unvented is a higher pressure than the heating system
Yes I would expect that, but also by the same principle the dirty water from the heating system (assuming the coil did split/perforated) would also come into the tank.

Baths filled from the tank are not clear water when its been in the tank for a while or the hot tank has been heated from the central heating system. if the tank is emptied immediatly emptied immediately after the water is clear.

If the the main water supply coming back on had stirred up the tank, surely that second flush out would be dirty too.

I come back to empty the tank after a few hours and it is dirty again.

Surely after a dozen full baths (to overflow) if the tanke was dirty from stirring up, or dirty water coming in once the leak in our neighbouring street was fixed , surely it would be clean by now.

I have been watching the pressure gauge all weekend, cant say I’ve noticed an general increase or decrease
I just feel like I could be slowly replacing the dirty central heating system with clear water from tank refills, and this isnt the behaviour of the coil being intact and slowly flushing the hot water tank clear.
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