Lost hot water pressure to a mixer tap

[rolyatescort]

Hi All,

My bath has a mixer tap on it, is one of those that also has a shower head. The cold is fed from a loft tank almost directly above, the hot is fed from an immersion tank on the same level.

The pressure of the hot water has always been relatively good, though would drop to almost non-existent if the cold was switched on also.

A few weeks ago, I was using the shower to wash the wall tiles with, I had the hot running, I then turned the cold on to get the extra pressure I needed to rinse the tiles off. At this point both the hot and the cold taps were fully open, though due to the pressure difference only cold was coming out, I know this was daft but I wasnt thinking. After a couple of minutes of this, I got a call from my neighbour to say that water was streaming out of the overflow and I mean streaming out.

Ever since I have had very little pressure from the hot tap. All other hot taps in the house are fine. I assume that I have either broken something or introduced an airlock or similar.

Could someone please tell me how to sort it as it is taking about three weeks to fill a bath at the minute!

Thanks in advance

 

[JohnD]

The cold is fed from a loft tank

How sure are you that is true?

you said water was coming out of the overflow (what overflow?)

this usually mean s that the cold is fed from the mains. It is not unusual under these circumstances for a mixer tap such as a shower to let high-pressure mains run backwards up the hot pipe.

 

[rolyatescort]

The cold is fed from a loft tank

How sure are you that is true?

you said water was coming out of the overflow (what overflow?)

this usually mean s that the cold is fed from the mains. It is not unusual under these circumstances for a mixer tap such as a shower to let high-pressure mains run backwards up the hot pipe.

Well there is a tank in the loft with a mains feed to it, that has to be drained in order for me to work on the system, ballcock tied up, etc. The tank is directly above the immersion tank, so could theoretically feed that?

The overflow is from the loft so assumedly from this tank.

Thanks

 

[JohnD]

I don't understand your reply.

Is the cold feed to that bath mixer from the tank, or from the water main?

I particularly ask this because you said

At this point both the hot and the cold taps were fully open, though due to the pressure difference only cold was coming out,

also

The overflow is from the loft so assumedly from this tank.

can you go and have a look please to test your assumption.

 

[rolyatescort]

right, in the loft there is one smaller tank with a larger tank above, both appear to be mains fed, but, both the infeed and outfeed pipes from these tanks route through the same place. Which is, down behind the immersion tank, directly below, feeds going to the top of the immersion tank, which also feeds the hot pipe to the shower, other pipes run to the floor, presumably to feed hot and cold throughout the house.

Overflow is definitely from the highest and largest tank.

Apologies I cannot offer more than that as I cannot see where the pipes route to due to layout of the house.

By all means if you have any more questions I will try my best to answer them.

Thanks

 

[JohnD]

Is the water-mains stop-cock readily available? It might be near the front door, or in the kitchen. If you turn it off for a few minutes, see which taps stop working. The kitchen cold tap should, the bath cold tap might. All the hot taps should continue working, fed from the tank

This is very relevant to working out what is wrong

BTW the big tank should feed into the bottom of the HW cylinder, supplying water for the hot taps. the small tank will be the Feed & Expansion for the boiler and the water which circulates round the radiators and the coil in the cylinders; it is a closed circuit and does not mix with the tap water. It probably connects with a larger pipe that goes into the cylinder, but this is a separate connection.

 

[rolyatescort]

Is the water-mains stop-cock readily available? It might be near the front door, or in the kitchen. If you turn it off for a few minutes, see which taps stop working. The kitchen cold tap should, the bath cold tap might. All the hot taps should continue working, fed from the tank

This is very relevant to working out what is wrong

BTW the big tank should feed into the bottom of the HW cylinder, supplying water for the hot taps. the small tank will be the Feed & Expansion for the boiler and the water which circulates round the radiators and the coil in the cylinders; it is a closed circuit and does not mix with the tap water. It probably connects with a pipe that goes into the cylinder, bit this is a separate connection.

The cold stops and the hot continues being fed from the tank.

Thanks

 

[JohnD]

Aha!

If the cold bath tap stops when you cut off the water-mains stop-cock, then that tap is fed from the mains. This will be higher pressure than the tank-fed Hot tap.

This is an undesirable way to feed a mixer tap, since it is pretty well impossible to adjust the mixed temperature properly, and cold mains water can flow up the hot pipe into the hot cylinder.

It is possible that your shower has a non-return valve in the hot pipe to prevent this happening, it may possibly have closed when you were washing the walls. Normally they spring back, but I suppose it might have limescale or something in it. If you can post some pics of the shower mixer and the pipes feeding them (probably under the bath) someone may recognise it.

BTW does the bathroom Basin hot tap still work OK?

 

[rolyatescort]

Aha!

If the cold bath tap stops when you cut off the water-mains stop-cock, then that tap is fed from the mains. This will be higher pressure than the tank-fed Hot tap.

This is an undesirable way to feed a mixer tap, since it is pretty well impossible to adjust the mixed temperature properly, and cold mains water can flow up the hot pipe into the hot cylinder.

It is possible that your shower has a non-return valve in the hot pipe to prevent this happening, it may possibly have closed when you were washing the walls. Normally they spring back, but I suppose it might have limescale or something in it. If you can post some pics of the shower mixer and the pipes feeding them (probably under the bath) someone may recognise it.

BTW does the bathroom Basin hot tap still work OK?

Just to clarify, this room has two showers in it, so when i talked about the shower that is next to the immersion tank and sharing pipework, that is seperate to the shower in my initial post which is fed from the mixer tap on the bath. The shower not on the mixer tap is still fed from the system, i.e. not an electric or pump driven shower.

Unfortunately i cannot show pictures from underneath the bath, though am certain that it is just hot and cold pipes feeding the mixer tap. The pipework to the seperate shower is more complicated so more than likely contains a valve as you surmise.

Both the bathroom basin and the seperate shower have good pressure, no different to that which they had before the issues with the bath hot water pressure.

so if the system is as you believe it to be from what i have told you and the mains cold has fed back into the hot through this mizer tap arrangement, is there a remedy?

Thanks

 

[JohnD]

apart from a possible non-return valve either in the bath/shower mixer, or in the hot pipe, I can't imagine what the problem is. It doesn't sound to me like there is an air lock.

If you are able to turn off the hot and the cold supplies, you could take the top off the hot tap part (as if you were going to change the tap washer) and inspect it for dislodged, jammed or faulty parts, such as the washer having come off and got stuck in the port below, or the screw-down part having come off its thread; also try turning the water supply back on and verifying that it squirts out of the top of the tap in a healthy fountain. This is also likely to wash out any obstruction or air bubble in the pipe. There are not many working parts in a tap. If you dismantle the cold side too you can compare them and look for any irregularities.

If you take it apart, have a new 3/4" tap washer and some silicon grease handy for reassembly, and give the internal parts a good clean with a tooth brush and a nylon pan scourer. I also like to put new PTFE tape on the threads where the top part screws into the mixer body.

 

[rolyatescort]

apart from a possible non-return valve either in the bath/shower mixer, or in the hot pipe, I can't imagine what the problem is. It doesn't sound to me like there is an air lock.

If you are able to turn off the hot and the cold supplies, you could take the top off the hot tap part (as if you were going to change the tap washer) and inspect it for dislodged, jammed or faulty parts, such as the washer having come off and got stuck in the port below, or the screw-down part having come off its thread; also try turning the water supply back on and verifying that it squirts out of the top of the tap in a healthy fountain. This is also likely to wash out any obstruction or air bubble in the pipe. There are not many working parts in a tap. If you dismantle the cold side too you can compare them and look for any irregularities.

If you take it apart, have a new 3/4" tap washer and some silicon grease handy for reassembly, and give the internal parts a good clean with a tooth brush and a nylon pan scourer. I also like to put new PTFE tape on the threads where the top part screws into the mixer body.

Thanks for that John, I will give that a go, I have tape, washers and grease ready, just didn't want to bother doing that, if there was something else potentially to blame.

Thanks for all your help