Hot water back flow

Gary and Kerry · Guru

Hot water back flow

twobob · Guru

Gary, not wishing to state the blooming obvious, its a pressure build up, as you will know, but why?

I will have a crack at an answer, and see if that helps

All HWS have a safety relief valve, to prevent over pressure from the heated water. This is normally set higher than mains pressure. I do not think it is this, but maybe check it operates.

When on tank water, any over pressure will be returned to the tank, so you would not notice this.

If I am right, on gas, the system heats to a certain point, but only cuts in to full, when in use, ie water flow, so again, you would not notice the problem.

So my conclusion is that on electric, it heats to full temp, and the pressure, while below the relief valve setting, is greater than the abilities of your fittings.

The answer may be a check (backflow) valve on the van, but only if the releif valve functions correctly.

Maybe someone with better knowledge has an answer

Gary and Kerry · Guru

twobob wrote:

Gary, not wishing to state the blooming obvious, its a pressure build up, as you will know, but why?

I will have a crack at an answer, and see if that helps

All HWS have a safety relief valve, to prevent over pressure from the heated water. This is normally set higher than mains pressure. I do not think it is this, but maybe check it operates.

When on tank water, any over pressure will be returned to the tank, so you would not notice this.

If I am right, on gas, the system heats to a certain point, but only cuts in to full, when in use, ie water flow, so again, you would not notice the problem.

So my conclusion is that on electric, it heats to full temp, and the pressure, while below the relief valve setting, is greater than the abilities of your fittings.

The answer may be a check (backflow) valve on the van, but only if the releif valve functions correctly.

Maybe someone with better knowledge has an answer

Thanks Bob,
I have had a closer look this morning , there is a one way valve between the HWS plumbing and the fill point and so i think this is probably be the culprit.
Will only turn HWS on just before use whilst connected to mains if i can't get a replacement before getting home.
We don't spend a lot of time in CP's so shouldn't be a major issue.

Cruising Granny · Guru

I have found if I only turn the main supply tap on about half flow and not flat out it doesn't blow off the connections.
Also make sure your connections are all firm. Brass has a longer life.
It's a bit of trial and error. Good luck with that. Cheers Chris

Basil Faulty · Guru

Has to be the non return valve..... Have you tried cold showers?
Have you checked the anode?

troublemaker · Newbie

Ok most units have a relief valve that should drip some water as it heats up to relieve excessive pressure... .....make sure this is working by observing that water drops from the relief pipe.
But. . . .. your problem is the check valve in the piping

It wont be the anode. . ..that is only there to stop corrosion and rust.

Basil Faulty · Guru

troublemaker wrote:

Ok most units have a relief valve that should drip some water as it heats up to relieve excessive pressure... .....make sure this is working by observing that water drops from the relief pipe.
But. . . .. your problem is the check valve in the piping

It wont be the anode. . ..that is only there to stop corrosion and rust.

Yes I meant have you checked the anode to make sure you still have some anode left, they get used up quickly.