Shower temperature drops off then back to hot

breaking_free

Hi all.

I have a Potterton Heatmax combi boiler and two mixer showers (one's an ensuite).

Whenever I take a shower the water comes out nice and hot, then about 30 seconds in it goes lukewarm, then back to hot again and stays hot for the rest of the shower. So to be clear, the temperature drops exactly once during each shower. The exact same is true of the ensuite shower.

I have British Gas home serve and they've come round three times now to look at it. The first guy said it was the heat exchanger, so he put a new one in. The second guy said he'd put a sensor in - still no change. The third guy said that perhaps the thermostat on each of my showers was battling it out, as it were, with the boiler to set the temperature. Can't say I think too much of that explanation as if it were true then everybody with a combi boiler and mixer showers would have this problem.

I'm stumped. Any ideas what could be causing this to both showers?

beaker141

I had similar once but it would go cold a few times during the shower - mine was the diaphram had perished and needed replacing.

I'd eliminate the showers - what happens if you just run a hot tap - does the same occur ? If the shower is on its hottest setting - does it still happen ?

When the "experts" did their respective fixes - did they test it before leaving you or was it a case of "I've changed that part, still happens, you'll have to raise another call to try something else" !

Edit - The Diaphram in the boiler !

breaking_free

Thanks for the pointers. The shower diaphragms are unlikely to be the problem as both showers are brand new.

I'll try running the hot tap as you suggest to see if the problem occurs there.

As to what happened when the 'experts' did their respective fixes, yup, exactly as you've put it. No testing, just "That oughta fix the problem and if it doesn't call us again".

"Sigh".

SplanK

breaking_free wrote: »

Thanks for the pointers. The shower diaphragms are unlikely to be the problem as both showers are brand new.

Just because something is brand new does not mean its not faulty

Rubidium

breaking_free wrote: »

Thanks for the pointers. The shower diaphragms are unlikely to be the problem as both showers are brand new.

I'll try running the hot tap as you suggest to see if the problem occurs there.

As to what happened when the 'experts' did their respective fixes, yup, exactly as you've put it. No testing, just "That oughta fix the problem and if it doesn't call us again".

"Sigh".

The diaphragm is in the boiler!

This shows that BG Homecare are not 'experts' and are in fact useless with their poke and hope approach to fault finding. They are simply wasting your time, get someone in who actually understands your boiler.

gingernut352000

We had similar and hot tap in kitchen went cold then hot took longer to happen than the shower our fault was secondary heat exchanger not the main one

breaking_free

gingernut352000 wrote: »

We had similar and hot tap in kitchen went cold then hot took longer to happen than the shower our fault was secondary heat exchanger not the main one

Very interesting. This possibility bears further investigation methinks - thank you for sharing.

southcoastrgi

I'm guessing the boiler is hot from having the heating on so it will put this straight to the hot water hence hot water straight away & may even have pre-heat, the boiler then takes time to reheat the hot water so it will reduce for a period of time & then settles down which is why you get constant hot water

breaking_free

Hi Southcoastrgi, thanks for the suggestion.

In fact I don't have the heating on in the morning. The first bit of heat in the house is created by me having my morning shower.

I tried Beaker141's idea this morning and turned on the hot tap. Guess what? No drop in temperature. I then ran the shower and no drop in temp.

My actual daily routine is this: turn on hot tap in bath to get the water up to temp, then turn it off and put shower on.

The next thing I'm going to try is turn the water heat down on the actual boiler. My thinking is that if the thermostat on the shower really is battling with the boiler to control the temp, then if I make the incoming water temperature pair up with the shower's expected temp no 'battle' should occur.

gmcl81

We called out AA home service for same problem and they shut down the boiler! That was a week ago and they say they are still "sourcing parts" ( for a 7 year old Vokera boiler) while we now have no heating or hot water! Now I would settle for a shower which occasionally runs cold!

breaking_free

Ooer gmcl81 that sounds no fun at all.

Well my 'turning the boiler heat down' experiment didn't work at all. And here's the thing - that temperature drop has gotten noticeable colder in the last few weeks. The problem is definitely getting worse and it's not my imagination i.e. I'm not just thinking it's colder because it's winter.