Perplexing plumbing puzzle - please pacify problem!

[Jonny2207]

I moved into a new build around 18 months ago, and I consider myself a competent DIYer. Before I ask the builder to come and look at my plumbing I wanted to get some opinion on an odd issue we've been having.

Our showers don't get hot (we've got two of them). It was most noticeable (probably because we used it more often) on one that the other. To the point that we asked Bristan to come take a look. 3 visits later, after replacing the cartridge and then the whole mixer unit, it is still the same. And we've now noticed the other shower is now much the same.

To add intrigue to the problem, the showers do get hot if you run a faucet tap first. I have tried this in different combinations with showers on/off and taps on/off and watched what happens to the screen on the boiler.

This is the results (with no other water sources on in the house):
Shower on > tap off: No activity on boiler
shower on > tap on: hot water on
tap on > shower on: hot water on
tap on > shower off: hot water on

So it seems that the shower on its own isn't 'drawing' enough water to kick start the boiler. Is that a thing?

The boiler is a 35kW Ideal Combi.

HELP ME! I'm going mad.

 

[CBW]

Yes, it does sound like there’s not enough flow for the boiler to recognise a hot water draw off. I’d be getting the builder back. You might even have crossed connections.

 

[oldbutnotdead]

There may be a pressure restrictor in the shower- have you still got the paperwork?

 

[durhamplumber]

I moved into a new build around 18 months ago, and I consider myself a competent DIYer. Before I ask the builder to come and look at my plumbing I wanted to get some opinion on an odd issue we've been having.

Our showers don't get hot (we've got two of them). It was most noticeable (probably because we used it more often) on one that the other. To the point that we asked Bristan to come take a look. 3 visits later, after replacing the cartridge and then the whole mixer unit, it is still the same. And we've now noticed the other shower is now much the same.

To add intrigue to the problem, the showers do get hot if you run a faucet tap first. I have tried this in different combinations with showers on/off and taps on/off and watched what happens to the screen on the boiler.

This is the results (with no other water sources on in the house):
Shower on > tap off: No activity on boiler
shower on > tap on: hot water on
tap on > shower on: hot water on
tap on > shower off: hot water on

So it seems that the shower on its own isn't 'drawing' enough water to kick start the boiler. Is that a thing?

The boiler is a 35kW Ideal Combi.

HELP ME! I'm going mad.

Is your stop tap fully open?.Or as said. .crossed connections somewhere..or dodgy mixer taps

 

[mattylad]

Is the isolating valve for the shower water connections fully open?

 

[terryplumb]

You stated that you used one shower more than the other ,and have lived there for 18 months ,so I assume the shower must have worked well for a period ? If this is so and your problem surfaced more recently ,I would suspect a problem with the boiler ,not shower valves that have been replaced.

 

[algas]

My Daughter had a similar problem when she rented a flat that had just been re furbished, after three visits from different plumbers I went for a visit She in London me in Devon, the shower flex was one from an electric shower, internal bore about 6mm and the head was no better, I replaced the flex with a 12mm internal bore and drilled some extra holes in the shower head,hey presto works fine, the old set up wasn't allowing enough water through to trigger the flow sensor on the boiler, she asked the agents if they would pay me to fix it, that was a negative so when she moved out she took the new parts and left the shower not working for the incoming tenant, I wonder how many visits from plumbers it took to sort it, should have just paid me!

 

[Jonny2207]

All, thanks for all of your advice. I hope you don't think i'm ungrateful but i haven't checked this thread for a while after I took "The Novice"'s advice and contacted the plumber that fitted the boiler. Its now resolved but I though I should post the solution in case others have this same problem.

Short answer: It was the pressure reducing valve from the mains, located under the sink, set too low.

Long answer: It was set to just a tad under 2 bar. It seems that this was sufficient for the plumber to sufficiently ensure that the showers were working - when originally fitted! All it then took was a little timescale on the shower heads, in the pipes, etc, to start to reduce the flow rate. The plumber only diagnosed this on the second visit, after we cleaned the heads, removed the flow restrictors, etc. on the first visit. It worked when he left but it was still temperamental - working better when the shower head was below the height of the mixer bar.... BINGO!.... the flow rate was still too low (but only just).

So we changed the pressure reducing valve to 3 bar and everything works perfectly! Only took 5 visits from plumbers to sort out such a simple problem. If i can help others avoid this problem, then great!

 

[Jonny2207]

...she asked the agents if they would pay me to fix it, that was a negative so when she moved out she took the new parts and left the shower not working for the incoming tenant, I wonder how many visits from plumbers it took to sort it, should have just paid me!

Whilst I appreciate why you did this, I do feel very sorry for the incoming tenant!