Shower Problems (but only in the morning?)

[Beev]

We've just moved into a new house with a combi-boiler system. The shower is fitted with what looks like a thermostatic mixer valve (although it could be presure balanced - Is there an easy way to tell from the outside?). The only branding on the valve and shower is "Marti" which I've yet to identify on the internet.

The shower worked fine when we moved in (late July) but in recent weeks has been running cold on a morning - the lights on the combi indicate that no hot water is being demanded. The only way to get a warm shower is to turn on the hot tap in the bathroom sink, wait for the hot water and then revert to the shower to get the 40 seconds or so of hot water in the pipes.

I was all set to replace the valve but I am not sure that this is the problem because the shower works perfectly during the day and evening. Is it possible that increased water usage in the neighbourhood on a morning (kids going back to school etc) is in some way reducing my water pressure and causing problems for my shower valve?

If so is there anything that I can do? Are there shower valves that will be able to cope with this problem?

Any thoughts would be much appreciated because the girlfriend is becoming increasingly frustrated by the situation!!

 

[Bahco]

You have answered your own question
Shower works perfectly except in the morning suggests a drop in pressure.
Fill a bucket of water in the morning and night and compare how long it takes to fill.
If morning is significantly longer to fill you will know it is indeed a pressure drop.
Let us know the result

 

[Beev]

Thanks BAHCO,

I will do the bucket check but it'll be Monday before i can post the results.

However, as you note I am fairly sure the issue is the water pressure in the morning. The flow rate from the other taps is noticably slower. However I'm struggling to understand why all the other hot taps in the house can supply hot water but the shower can't? Have I got a duff valve or will any valve be affected by this problem?

Assuming that it is the pressure, is there anything that I can do to rectify the problem?

 

[Bahco]

When you run your shower in the morning is it the only appliance drawing hot water as combis can only supply one hot outlet at a time .
Do you have a washing machine going at the same time
If not I can't see it being the shower valve if as you say it works perfect at all other times of the day.
Chris R should be online soon, maybe he can shed some light on this

 

[Beev]

There should be no other demand for any water (hot or cold) as no taps or appliances are on. Plus the combi isn't firing so it cannot be supplying hot water anywhere else.

For some reason the shower just isn't demanding hot water from the combi which makes me think that the thermostatic valve is pressure sensitive and will not operate below a certain pressure. But is this normal or does it signify a fault in the valve Is there any straightforward way to measure the water pressure

thanks for your thoughts thus far and here's hoping Chris R can assist.

 

[RKB]

I've got exacltly the same problem as this. Hot water only if you turn the taps on full - shower is cold.
Boiler is a combi.
I concluded that the shower wouldn't work because the cold supply to the therm control was reducing the available pressure for the hot side.
The problem has been diagnosed by a pro as a faulty diverter valve in the boiler not detecting low hot water demand, only high demand.
Hope that helps .. although I don't think I've explained this very well

 

[Bahco]

RKB
That does sound like a possible explanation but in this instance there is only a problem in the morning.
If it was a faulty diverter valve then it would not work at other times of the day which it seems to do
Hopefully the other guys will help

 

[oilman]

Beev's problem seems to be low pressure in the morning. This will mean the flow to the shower is too low to operate the flow switch in the boiler. If you open a tap the flow is high enough to operate the switch so you get hot water. To get the hot water, you may be able to open a tap a little to get the boiler to operate, while allowing enough water to get to the shower.

Long term solution is to get larger incoming water pipe, or fit a hot water tank and pump the shower or even fit an electric shower. These things might not be ideal, but you have to work with what there is.

 

[ChrisR]

Most things have been covered well. It would help if we knew what boiler it was, how old...!
Diverter Valves often underperform before failing completely. a small hole in a diaphragm and/or a sticking mechanism could mean more water flow would be needed to get it open.
Could very well be a restriction in the mixer, but try the head. Unscrew the shower head and see if the flow from the hose is greater. Maybe it just needs descaling. May also be that a screwed up liner in the shower hose is doing it. Take it off and stretch it straight (needs help!)- you should be able to see through it.
Many fixed shower heads have flow restrictors in them too.
COuld also be the filter in the combi is slowing things bit. It willalso probably have a flow restrictor designed to make sure you get water which is hot enough in the winter. If you get that taken out you'll get more water but at a lower temperature.

Think yourself lucky that when it is working, the temp doesn't oscillate between hot and cold - which is typical of combis which are struggling.

 

[Beev]

Thanks to everyone for their thoughts.

I'll have a play around with the shower tonight and ensure there is nothing restricting the flow etc.

If not it sounds like I'll need to get a plumber out to have a look at the diverter valve. Is that the kind of spare that a plumber should carry

Combi by the way is a Worcester something or other and we were told that it was installed in the mid-nineties. I'll post the model number tomorrow.

 

[oilman]

Is that the kind of spare that a plumber should carry

Some people don't carry very much. I've been called out by boiler servicing guys because they don't do combies.

 

[Beev]

I've tried all of Chris R's suggestions and the shower still went cold shortly after 7 this morning. The obvious solution that we get up earlier was met with a particually frosty response from the girlfriend.

I'll get the valve replaced (thanks for your comment oilman - I'll make sure the plumber knows what he is dealing with (and the likely parts) before he comes around) and hopefully that will solve it.

In response to an earlier question - the combi is a Worcester 9.24 RSF and we've found some paperwork that seems to suggest that it was installed in 1994.