Hot water smells in unvented system

[Pablosammy]

Bear with me, average homeowner here.

My hot water smells. I can only really notice it in the shower when it's steaming away, but there is a distinct chemical smell that reminds me of corrosion inhibitor.

We're in a new build with an unvented hot water system. I haven't had to top up the dosed side of the system for quite a while, although I don't know if that's a symptom or just whether it's nice and pressure tight.

My immediate thought is that the heating coil in my hot water cylinder is leaking. Our mains pressure by the time it gets upstairs is 1.5 bar, which means I can't tell if the dosed side is following my mains supply pressure. My plan is to test this theory by isolating the cold water feed at the stopcock, depressurise that side of the system by opening a tap, and then seeing whether the closed loop slowly drops in pressure. I assume I'd have to manually open the hot water coil inlet valve for this test to work, obviously I'll turn the boiler off first.

My (possibly preferred) alternative is to depressurise the heating circuit and see whether it repressurises.

Is there a better way to test this? Any obvious holes (no pun intended) in my plan?

 

[Sharp Point]

Yes, depressurise the heating. It could take a while to fill the heating up if it’s a pin though and it is quite cold.

 

[Scott_D]

Could it be the shower drain that smells?
It would be the same water that comes out if all hot taps, try the basin next to the shower.
Try taking off the shower head and hose and give them a deep clean.

 

[SimonG]

It's not the coil. The cylinder will be at a greater pressure than the heating circuit. Sounds like bacteria, possibly due to incorrectly stored hot water, that is temp set too low.

 

[Pablosammy]

It's not the coil. The cylinder will be at a greater pressure than the heating circuit. Sounds like bacteria, possibly due to incorrectly stored hot water, that is temp set too low.

Is the cylinder not at or below mains pressure? If it isn't, how does it fill?

Our heating circuit and mains pressure are the same when cold, and when the heating circuit is hot it's 0.2 bar higher.

I've let the heating system down to 0.8bar or so, I'll monitor over the next few hours.

 

[SimonG]

You would get the same problem as you would have on a combi with a perforated secondary heat exchanger. Which your not. Bacteria.

 

[Pablosammy]

You would get the same problem as you would have on a combi with a perforated secondary heat exchanger. Which your not. Bacteria.

Wouldn't bacteria create a sulphur smell, rather than a chemical smell? I'd trusted my nose, but please educate me if I'm wrong!

 

[SimonG]

Education costs money in this game.

Here endeth the free lesson.

Good luck.

 

[Pablosammy]

Education costs money in this game.

Here endeth the free lesson.

Good luck.

Thanks for the help.

 

[Pablosammy]

Well, forgive me for being sceptical about Simon's 'educated' diagnosis, but the heating circuit pressure has risen by 0.45 bar since yesterday with the filling loop disconnected. It's now approaching the cold water supply pressure (a measly 1.3 bar at the moment). System temperatures are the same as at the point I measured it yesterday.

Just for the record, Simon, I may not be a plumber but I am a professional engineer who operates industrial scale pressurised water systems, heat exchangers etc. day in, day out. In the time you took to type your last reply, you could instead have written a brief explanation of your reasoning, I'm sure my pretty little non-plumber head would have understood. Instead you chose to be arrogant and patronising.

Time for a professional to take over the reigns, thanks for all the assistance.