Hot water and old boiler

Yazmina

The hot water in our house fluctuates a lot.  In the kitchen, bathroom and cloakroom mixer taps it takes several minutes for the hot water to come through, and a lot of cold water is wasted. Then once the hot water comes through, it lasts a little while then goes cold again.  The water temperature on the boiler is turned up, but it makes no difference.  

The boiler is over 10 years old and could be replaced, but we're holding on in case it's got a few more years left in it.  Could the old boiler be the cause of the fluctuating water temperature? We've saved up for the new boiler, so if it will solve the water problem we'll get it replaced asap.

Thanks.

FreeBear

Combi boiler or is there a separate hot water tank ?

I have a combi boiler installed at the front of the house directly under the bathroom - Almost instant hot water from the taps up there. With the taps in the kitchen (at the rear of the house), I need to run the water for quite a long period before getting hot water. Such is the delay, I find it more efficient to boil the kettle when doing the washing up.

When I had an ancient gravity fed hot water tank (in one of the bedrooms), getting hot water from any tap required a wait...

Albermarle

FreeBear said:

Combi boiler or is there a separate hot water tank ?

I have a combi boiler installed at the front of the house directly under the bathroom - Almost instant hot water from the taps up there. With the taps in the kitchen (at the rear of the house), I need to run the water for quite a long period before getting hot water. Such is the delay, I find it more efficient to boil the kettle when doing the washing up.

When I had an ancient gravity fed hot water tank (in one of the bedrooms), getting hot water from any tap required a wait...

I do not have a combi boiler, but have the same issue with it taking ages for hot water to come through the kitchen taps.
So also usually just boil a kettle.

Yazmina

Combi boiler, upstairs in a cupboard next to the bathroom. 

FreeBear

Yazmina said:

Combi boiler, upstairs in a cupboard next to the bathroom. 

This poster had a similar sounding issue -> https://forums.moneysavingexpert.com/discussion/6571468/boiler-keeps-going-hot-and-cold - Don't know if the problem was fixed though...

ThisIsWeird

Hi Yazmina.
So it's a combi, and positioned close to the bathroom.
I did wonder if it was down to distance, and perhaps the reuse of old 22mm copper pipes (larger amounts of cold sitting water to shift), but that doesn't fit, and also wouldn't explain the water running cold again, which it obviously shouldn't do. The hot-cold-presumably repeating symptom suggests an actual boiler issue, and the classic cause is a blocked P2P or 'secondary' exchanger.
Q's:
Make and model of boiler, please?
Has it always been like this, or has it started happening recently?
Is there a magnetic filter fitted on the return pipe to the boiler, usually a cylindrical object 6-odd inches tall fitted under the boiler?
Something to check: you'll need someone watching the boiler, and someone in the adjacent bathroom, within earshot of eachother. A timer would be handy.
Open hot tap to a decent flow, and let boiler person know - start timer. Q's;
Does the boiler respond instantly? What does it do? Does it have a 'flame' or 'burner' symbol or light? Is it on?
How long does it take for warm, and then properly hot water, to come out the tap? What is the boiler doing throughout this - the burner should be constantly lit - is it?
Keep it running. When does it run cold again? What is the boiler doing before it runs cold?
If you keep it running for another 30+ seconds, does it begin going warm again?
Please report back.

Yazmina

This is the boiler.  Apparently it's a Vitodens 100-w.  The operating instructions are dated 1/2012. 🙄



As you can see, there is no light.  When the taps are turned on it makes a noise as though it's firing up.  The bathroom basin water was warm straight away.  The shower took 8 seconds to get warm, then a minute to get hot.  It stayed hot for over 2 minutes. 

The burner indicator goes up to certain point (9.9*c), then back down to zero. But it does the same thing when the water is off. 

Thanks.

ThisIsWeird

When was it last serviced? In particular, when was that Magnaclean opened and checked?

Yazmina

September 24. The report doesn't mention the magnaclean.  I don't think it's been checked in recent years. 

Ectophile

Water going alternately warm and cold could be a clogged heat exchanger.  It will struggle to heat the water properly, and eventually overheat and shut down as it's failing to transfer the heat from the burner to the hot water flow.

It may then start cycling on and off trying to keep the water inside the boiler down to an acceptable temperature.

Yazmina

Ectophile said:

Water going alternately warm and cold could be a clogged heat exchanger.  It will struggle to heat the water properly, and eventually overheat and shut down as it's failing to transfer the heat from the burner to the hot water flow.

It may then start cycling on and off trying to keep the water inside the boiler down to an acceptable temperature.

Is this worth repairing on a boiler so old?