Has my hot water cylinder coil broke?

[Dave18183]

So there has been some developments.

Last tuesday I flushed the tank out with a hose from the drain out point to outside, several times over (fresh water to the tank isolated), hot tap open to vent it, blasted with cold water when empty to clear any sediment at the bottom of the tank assuming this is the issue that has been suggested (On here and by my local plumber).

I closed the tank drain valve, and left the tank empty for several hours to watch for a pressure change on the boiler. It Dropped about 0.2 bar over the 5 hours in the afternoon to evening. Put this down to a natural loss from the system still cooling from the heating on in the morning, and the day/house getting cooler.

Hot bath water still wasnt clean but better, so continued with tank flushing the next day. Even tried a back flush but only at mains pressure. With the tanke empty, this time left a tub under the tank drain point, and left the drain valve open. My thoughts were if the coil was split, surely it would be pi$$ing out water into the empty tank. An hour passed, not a drip or the sound of one in the tank.

Next day hot water was clean, finally and end to this. Seemed it was just dirty water from after the nearby street water leak and sediment stirred from the bottom of the tank. We have all showered and our little one bathed in it twice. The central heating has been on and off throughout, but not as much as weather is getting milder. We still have a drip from our overflow pipe downstairs but myself and plumber put this down to the cold pressure relief valve not re-seating after I clicked it over (probably the first time in 20 years).

Anyway..... 5 days on, tonight run a bath and get this below

Pressure at the boiler was a little low at just less than 1 bar with heating off but hot water on. Opened the filling loop and it immediately jumped 0.5 bar.

So. All things considered. Is this still dirty mains water, sediment stirred after numberous tank drains. Or is it the coil.

Any help would really really be appreciated.

 

[Dave18183]

Change the cylinder if you want to, but if the coil had gone your heating would be at the same pressure as your cold main so the gauge would be over 3 bar all the time and your boiler PRV would be passing water all the time.

PRV as been passing water, hence the constant drip/trickle out to the overflow downstairs.

but pressure at the boiler gauge seems to have gone down a bit after several days and as per my previous post, opening the filling loop it went up by 0.5 bar in seconds

 

[ShaunCorbs]

I would ring the water board and check there still not doing work in the area as they could be replacing water mains etc

 

[Dave18183]

I would ring the water board and check there still not doing work in the area as they could be replacing water mains etc

Thanks for your reply. There are no issues registered in the area on united utilities, but I will ring them.

what I don’t get about the posts on here about dirty mains water is I have drained down the tank and tried to flush it tank, several times. Each time it being filled with fresh cold water which is coming into the house clean....... but the water is coming out of the tank dirty when it’s left in their any given time.

 

[Dave18183]

Just drained out the hot water tank. For info central Heating went off about 90 minutes ago hot water about 50 minutes ago.

It took about 30 minutes to empty the hot water tank/cylinder meanwhile the gauge on the boiler has dropped from abou 1.3 bar to about 0.4 bar.

still just dirty mains water?

 

[Dave18183]

Gauge pics

 

[Ric2013]

I'd be wanting to pressure test the coil at this point, to be certain what is going on. More simply, while the boiler is cold and the cylinder is empty, if you top the pressure back up to 1 bar, does it drop again?

It has been suggested by others that if the cylinder were leaking into the primary circuit (boiler water), the pressure would be over 3 bar and the PRV (on the boiler) would blow. But we don't know what the OP's mains pressure is: it might not even be as high as 3 bar (can be as little as 0.7 Bar).

Also, could the OP please run a bathful of COLD water? This would give us an idea of the quality of the mains water entering the house.

 

[Dave18183]

I'd be wanting to pressure test the coil at this point, to be certain what is going on. More simply, while the boiler is cold and the cylinder is empty, if you top the pressure back up to 1 bar, does it drop again?

It has been suggested by others that if the cylinder were leaking into the primary circuit (boiler water), the pressure would be over 3 bar and the PRV would blow. But we don't know what the OP's mains pressure is: it might not even be as high as 3 bar (can be as little as 0.7 Bar).

Also, could the OP please run a bathful of COLD water? This would give us an idea of the quality of the mains water entering the house.

Thanks for your reply Ric2013.

That is the thing that confuses me. Couple of people on have said the boilder pressure increase if the coil was perforated in the unvented indirect hot water cyclinder/tank. Two local plumbers Ive spoke to have suggest it would decrease.

cold water bath picture just run attached

 

[Chuck]

Couple of people on have said the boilder pressure increase if the coil was perforated in the unvented indirect hot water cyclinder/tank. Two local plumbers Ive spoke to have suggest it would decrease.

There are (at least) two types of leak with different behaviours.

Most of the discussion in this thread assumes a simple bidirectional leak, such as one caused by pin-hole corrosion or a split in copper tube. The flow through such a leak depends on the pressure difference in a symmetric manner. I.e. positive difference causes flow in one direction. Reversing the pressure difference causes flow in another direction.

The second type of leak occurs when joint (solder or welded) fractures but is held normally closed by the springiness of the metal pieces being joined. Such a leak can exhibit unidirectional, aka 'diode', action. I.e. allow flow in one direction, in this case from CH to DHW, but not vice versa.

The second type is less common than the first type and can give rise to some puzzling behaviours.

Anyway, I suspect you have a 'second type' of leak. To diagnose, you either need to put tracer dye into the CH water or pressure test the cylinder coil.

 

[Dave18183]

Thanks Chuck, thats interesting thoughts. It doing my head in!

Afte a bit of a tank refill and emptying again I feel like it should be empty now but its still draing with not quite clear water and a very slight noticeable chemical film on the stop of the water.

Getting noises as it goes. Is this the sound of the coil draining into the tank?


Pressure has continued to drop at the boiler thought slowly. Down from 0.4 bar earlier to just over 0.2