hot water problem

[mickspangle]

Dear all,

 

curious problem this one. My hot water pressure cycles between high and low when any of the hot taps are on. Hot water comes out of a calorifier with a 3 bar pressure relief valve, and is filled from a regular 2 bar shurflow pump through a non return valve (to stop hot water getting back into the cold feed) - all fairly standard stuff I would have thought (and it certainly never used to cycle like this).

 

There is no accumulator.

 

I'm at a loss as to what is causing it. Could it be air trapped in the (horizontal) calorifier from when we've run out of water that is sitting at the top and causing the calorifier to behave like an accumulator? Anyone else experienced this?

 

cheers

 

Mick

[Big COL]

Dear all,

 

curious problem this one. My hot water pressure cycles between high and low when any of the hot taps are on. Hot water comes out of a calorifier with a 3 bar pressure relief valve, and is filled from a regular 2 bar shurflow pump through a non return valve (to stop hot water getting back into the cold feed) - all fairly standard stuff I would have thought (and it certainly never used to cycle like this).

 

There is no accumulator.

 

I'm at a loss as to what is causing it. Could it be air trapped in the (horizontal) calorifier from when we've run out of water that is sitting at the top and causing the calorifier to behave like an accumulator? Anyone else experienced this?

 

cheers

 

Mick

 

Hi Mick

 

If running out of water is the only change to the system then it's likely to be air trapped somewhere. Is the pressure relief valve higher on the calorifier than the hot water take off point? If so twist the knob on the relief valve and bleed the air out through it.

If not there should be a bleed point built into the calorifier.

[mickspangle]

Hi Mick

 

If running out of water is the only change to the system then it's likely to be air trapped somewhere. Is the pressure relief valve higher on the calorifier than the hot water take off point? If so twist the knob on the relief valve and bleed the air out through it.

If not there should be a bleed point built into the calorifier.

 

cheers Col...tried bleeding it via the PRV, but doesn't seem to work. I'll try bleeding it a bit more tonight. Thinking about it, it has to be related to the calorifier, as it doesn't happen to the cold supply.

[Keeping Up]

Do you have a thremostatic mixer valve, which combines the hot output from the calorifier with a cold feed to prevent scalding? I had similar symptoms and found that the mixer had a safety shut-off if the hot supply to it reached 80 degrees, so when the engine brought the water in the calorifier right up to max temperature, the mixer would shut down then let some through then shut down then let some more through, and so on. It could hav started to do this if your engine is for any reason running just a couple of degrees hotter than it was before. The clue was that the hot water supply worked fine if you let the water in the calorifier go cold (by not running the engine). The cure was to get a different (cheaper) model of mixer which didn't have the over-heat protection.

[smileypete]

Dear all,

 

curious problem this one. My hot water pressure cycles between high and low when any of the hot taps are on. Hot water comes out of a calorifier with a 3 bar pressure relief valve, and is filled from a regular 2 bar shurflow pump through a non return valve (to stop hot water getting back into the cold feed) - all fairly standard stuff I would have thought (and it certainly never used to cycle like this).

 

There is no accumulator.

 

I'm at a loss as to what is causing it. Could it be air trapped in the (horizontal) calorifier from when we've run out of water that is sitting at the top and causing the calorifier to behave like an accumulator? Anyone else experienced this?

 

cheers

 

Mick

May be the other way round, there was air trapped in the calorifer smoothing out the flow but it has now mostly gone.

 

The high-low pressure may be caused by the non return valve sticking. In any case if you have no accumulator you almost certainly don't need the non return valve.

 

High-low pressure can be caused by an iffy pump or electrical connection, but would affect both hot and cold taps so seems unlikely in this case.

 

cheers,

Pete.

[mickspangle]

Thanks for the advice. I bled the calorifier through the prv for a while to get rid of the air and that seems to have sorted it. I guess the title of the thread should have been 'how to turn your calorifier into a giant accumulator'.

 

On the subject of non return valves on cold feeds going into calorifiers, surely I need one to prevent hot water flowing out of the calorifier and back into the cold pipe every time I turn on the cold tap?

 

Edited for speeling and that

Edited December 12, 2009 by mickspangle

[nb Innisfree]

Thanks for the advice. I bled the calorifier through the prv for a while to get rid of the air and that seems to have sorted it. I guess the title of the thread should have been 'how to turn your calorifier into a giant accumulator'.

 

On the subject of non return valves on cold feeds going into calorifiers, surely I need one to prevent hot water flowing out of the calorifier and back into the cold pipe every time I turn on the cold tap?

 

Edited for speeling and that

 

Not necessarily, it may only be a small amount of hot water that has expanded back into the cold feed or you may not get anything, try it and see. Or you could maybe put in a separate cold feed to avoid fitting a NRV like in the picture, once installed it's less to go wrong and it avoids the need for an expansion vessel, ours works a treat.