Why's my water running hot and cold?

[eyedee]

My 2 floor semi detached has a strange issue that started a few years ago. Initially the problem was my first floor shower would run hot and cold during the summer only, but intermittently work better or perfectly well during the winter. For info, the shower is not electric and is simply fed by an ageing glow worm combi boiler in the kitchen beneath (which performs its central heating duties without issue).

When it first started happening during Summer of a few years back I blamed the shower thermostat. But then the following autumn I discovered that when I had the central heating on and running the shower wouldn't get cold. However it's not quite as simple as that, as when the the heating has beed used every day - on timed for a couple of weeks - the shower will remain hot even when the central heating isn't actually running.

Anyway, this past August I tried to turn the heating on to see if that helped, and it helped a bit - the water stayed hot for a bit longer, but it still got cold.

Now the colder Autumn/Winter months are here and things have gotten worse. At the beginning of the cold weather, and for the first time ever, we experienced the water in the shower AND the bathroom tap refusing to warm up until It had been run hot fully open for 5 minutes or so. Then it would go into the familiar rhythm of hot/cold.

That was a month or so ago, and now that the heating has been run every day for the past few weeks the bathroom tap and shower have started 'behaving' themselves again. The bathroom tap is working as expected and the shower generally stays hot, or at least only threatens to go cold before warming up again.

So where as I once assumed it was a shower thermostat issue (it started happening after our bathroom was refitted and a new stand alone shower installed in the place of an over bath extension pipe style shower) I guess it's actually a problem in the Combi Boiler?

I wondered if this pattern was recognisable and could be diagnosed to a faulty part? During the past 4 years I've had two service agents take a look One confirmed the external water pressure was fine but thought the pressure from the boiler was not as good as it should be, and the other said the issue was the shower thermostat - but I've obviously now experienced the refusal to get hot at the bathroom tap too.

It sure would be nice to figure out the cause if anyone has any experience in this kind of behaviour?

And thanks for taking the time to read quite a long post!

 

[CBW]

Sounds like an internal boiler fault to me. What make and model of Glow work is it?

 

[Newboy]

The probability is that the heat exchanger is scaled/partially blocked

 

[eyedee]

Sounds like an internal boiler fault to me. What make and model of Glow work is it?

It's called a Swift Flow 100. Looks kind of old but was considered a fairly decent boiler from what I can find out about it.

The probability is that the heat exchanger is scaled/partially blocked

Apparently it might be over 20 years old, so I think that could be the case! Thanks for pointing me in that direction, which led me to find another post where someone mentions the flow switch could potentially be a cause too?

 

[Newboy]

My money is still on the heat exchanger

 

[gasbusters]

X 2 heat exchanger.

Call a gas engineer to come and sort. It needs to be removed and descaled.i use brick acid, it just melts the scale away in about 30 mins.

However as its old, the seals may likely leak once you out it all back together, but emgineer will be aware of this so should come armed with new seals.

 

[eyedee]

Thanks guys. Ok, I'll get an engineer out to take a look. Turns out the boiler is 25 years old (!) so parts may be becoming scarce, but I guess seals are universal, so hopefully a clean and reinstall with new seals will be do-able.