overflowing hot water cistern

[feckem]

Hi
I have an oil fired boiler that heats both the hot water and central heating. A couple of weeks ago the system started to overflow the water coming out of the overflow is warm.

I have felt the feed pipe from the water cistern and its pretty warm which i take it means that hot water is making its way from the cylinder back up the feed pipe and over filling the tank in the loft. the hot and cold water systems work off two seperate tanks at the same level in the loft.

any ideas whats causing this problem?????????

 

[Softus]

Do you perchance have a shower valve that mixes mains-fed cold water with gravity-fed hot?

 

[feckem]

No shower valves at all shower is a single cold feed electric shower.

Alan

 

[Softus]

Do you have a washing machine that has both a hot and cold fill?

 

[feckem]

yes washing machine is duel fed. problem has been worse during the night when the hot water is not being used. but the machine has also been turned off at night could this still be the cause??????

 

[Softus]

It depends on what you mean by turned off.

Are there two separate hoses connecting the washing machine to two separate appliance valves?
Or is there a Y connector involved?

 

[feckem]

Two seperate hoses. both have check valves attached. and by turned off i mean just unplugged.

Thanks for this by the way

Alan

 

[Softus]

At this point it's worth clarifying the symptoms that you originally reported...

I have an oil fired boiler that heats both the hot water and central heating. A couple of weeks ago the system started to overflow the water coming out of the overflow is warm.

Is the overflow connected to a cold storage cistern (usually in the loft, and fairly large), or a feed and expansion cistern (usually in the loft, and fairly small)?

I have felt the feed pipe from the water cistern and its pretty warm

Is this the feed pipe from the cold storage cistern to the base of the hot water cylinder? If not, what is the pipe connected to at each end?

...which i take it means that hot water is making its way from the cylinder back up the feed pipe and over filling the tank in the loft.

I would tend to agree with your deduction, subject to the answers to the above questions.

the hot and cold water systems work off two seperate tanks at the same level in the loft.

Please explain more about this.

 

[feckem]

The system is connected to a cold water cistern in the loft its a fifty gallon tank.

The pipe is conected to the bottom of the hot water cylinder and comes direct from the cistern in the loft.

As to the last point you asked me to explain. for some reason i have two large (50gal) cold water cisterns one of which feeds the hot water cistern via the cylinder and the other feeds the cold water system ie bogs upstairs sinks etc. this system was put in a few years ago when i had an extension built.

the two tanks are not connected.

oh and i also have a small feed and expansion tank for the ch. no problems with this

Alan

 

[Softus]

The system is connected to a cold water cistern in the loft its a fifty gallon tank.

The pipe is conected to the bottom of the hot water cylinder and comes direct from the cistern in the loft.

Okey dokey.

As to the last point you asked me to explain. for some reason i have two large (50gal) cold water cisterns one of which feeds the hot water cistern via the cylinder...

I understand this, as long as you meant to write "hot water system".

...and the other feeds the cold water system ie bogs upstairs sinks etc. this system was put in a few years ago when i had an extension built.

the two tanks are not connected.

oh and i also have a small feed and expansion tank for the ch. no problems with this

OK.

On the information so far, the only mechanism for warm water entering the cold storage cistern, by backfeeding, is that cold water at mains pressure is entering the hot water distribution pipework that leaves the top of the DHW cylinder.

You can verify this theory by temporarily turning off the cold mains at your main stop cock. The overflowing should stop.

If it does, then you need to identify the point at which cold is leaching into hot. This can happen only where the two are close together, which means a mixer valve with unbalanced supplies, or a heat exchanger.

So, the pertinent question is: which taps, valves or appliances in your house are fed with mains cold water?

 

[feckem]

ill have to check which ones are fed by the mains. is it as simple as turning of the mains and seeing which taps / appliances stop running.

 

[Softus]

Indeed so!

What type of cylinder do you have?

Is it an 'ordinary' copper indirect type?

 

[feckem]

It is indeed a indirect cylinder. no electric element is fitted as the water is heated by the ch via a coil

 

[Softus]

What are your bath and basin taps like?

Any monoblocs that are fed from the cold main?

 

[feckem]

bath and basin taps all single. sink tap in the kitchen is one of the single lever mixer taps feed from cold mains as is the tap in downstairs wc.