black water from hot water cylinder

[mel]

hi,

i've looked on line for help with this but i'm struggling to come up with a complete answer. i have a back boiler behind the fire not sure what model but its way over 20 years old. hot water cylinder in airing cupboard upstairs that can be heated by gas or elec , one tank in loft. think looking at diagrams an indirect water cylinder

last night while heating and hot water was on tank sounded as though it was bubbling. turned the bolier off checked elec switch hadn't been turned on by accident (it hadn't ), tank still sounded as though it was bubbling so i opened the tap on the bath the water colour was fine and clear but scalding hot.

then there was some almight rumbling as though the house was coming down so i opened the tap on the bath bit more and then the water in the bath from the hot tap started to turn black smiliar to water in heating system. the rumbling contiued the whole time the water was running so i turned off the water to the tank and let the taps run dry the bottom of the bath was really black and gritty.

my guess is new cylinder as water heater coil in tank gone???

anyone have a rough guide how much this going to cost me???

any advise welcome

thanks in advance

melanie

[Andy Hall]

If it's a cylinder replacement only, then the price range is likely to be in the low £hundreds - i.e. in the £200-500 range depending on the work involved.

However, if the black water is, indeed from the boiler primary side it is indicative of corrosion going on in the heating system so it would be prudent for the boiler and radiators to be checked and the primary side to be cleaned out and corrosion inhibitor added. In any case the boiler should be checked and serviced if not done recently, so perhaps another £100-200 for this part assuming that nothing bad has happened to boiler and radiators are OK.

[Roger Mills]

If there is *really* only one tank in the attic, could it be a primatic cylinder (although I thought these usually have intergral header tanks)?

If it *is* a primatic cylinder, it sounds as if something has happened to make the primary and secondary circuits mix in a big way. I don't know enough about them to know whether this is fixable without replacing the whole thing. Inhibitor wouldn't be an option.

If it *is* a primatic, and *does* need replacing, it would be a good idea to replace it with a standard indirect cylinder with separate header and F&E tanks so as to separate the primary and secondary circuits completely - and

*then* to use inhibitor.

[Ed Sirett]

Agreed. I would add that unless the OP is totally skint the entire system is up for a total overhaul.

[Gav]

is there a thermostat on the cylinder,

if no could it be the boiler overheat senseor has failed and system expanded into the hot water header?

if so then maybe if you post the boiler details someone may give you a rough price for replacement or direct you to a stockist if it is replaceable!

[Mark]

I concur - although a total overhaul may not be necessary.

It's very likely to be a primatic cylinder. These rely on a kind of air bubble to separate the hot water/heating water. It is possible for the air bubble to collapse, which allows the circuits to mix. This may be your problem. Just drain down the entire system and refill first - this could fix the issue.

See

for more info on Primatic tanks.

If you have any spare cash though I would suggest that you replace the cylinder as Ed suggested. Primatic cylinders preclude the option to use inhibitor and are inefficient.

Good Luck, Mark

[able99]

thanks for all your help, the back boiler is an ideal cavalcade and we have been advised most likely its a problem with thermostat on that.? as we've been putting off getting new boiler for the last couple of years and are hoping to let our property next year. we're thinking this might be ideal time to do it as it needs fixing anyway.

thank you to everyone who replied it was a great help