Hot water and combi boiler

[Poorprincess]

Hi, we need some advice please as to what we should do with regards to our hot water.
We have a shower room downstairs where we need to run the shower for around 5-10 minutes before it gets nicely hot.
Our upstairs bathroom will take forever! I tend to run the hot tap to the sink first then once this becomes Luke warm I run the bath hot tap. This morning after 20 minutes I gave up waiting for any hot water to reach the bathroom.
Our boiler is over ten years old and is a combi boiler, oil. Should we contact a boiler engineer to see if he can improve this or is it something a plumber needs to deal with or is this just usual in old houses during the winter?!!

 

[Flyfisher]

Given that the combo boiler is about 10 years old, my immediate thought is to ask if the system has ever worked properly and if there have been any recent changes that might have affected its performance?

 

[Poorprincess]

Thank you for your reply.
We have lived here for about six years now and has always been like that really. We don't usually use the bathroom upstairs during winter months but just shower downstairs. During the summer it is better but still you need to wait about 10 mins to get good hot water upstairs. We just tend to live with it but if I thought it could be improved I would be very happy!

 

[Flyfisher]

Ok, so we're not really looking for something that might recently have gone wrong.

Assuming the boiler is regularly serviced and is in good working order it could be that it's simply not large enough for the job, I.e. not putting enough heat into the water, or that the heat is being somehow lost before it gets to the taps - or a combination of both. Are the pipe runs particularly long? Are the pipes well insulated? Is the boiler also trying to heat any radiators?

 

[Poorprincess]

The boiler heats 15 radiators too without any problem but only ever is either heating water or radiators. I don't think pipe work is that long, just upstairs and a room along from boiler room. Most of pipe work is boxed in but from what bit I have seen it isn't insulated. Could this be enough to stop water getting hot in the bathroom?
I had wondered whether the pipe work or boiler getting furred up with limescale could do it but would that not be the case?

 

[Zebra]

So will it heat up the hot water OK if the central heating is off? You said not, as you said it still takes ages in the summer. 10 minutes seems an awfully long time for a combi boiler to get water to the required temperature. If you run the taps and then feel the hot water pipe where it leaves the boiler, you should be able to identify whether the heat is leaving the boiler and getting lost somewhere, or never leaving the boiler at all. If you try this with and without the heating on, you should be able to identify whether the central heating is affecting it.

 

[Zebra]

Giraffe says one of the most common failure modes for a combi boiler is for the diverter to get sticky. There is only one burner, but there is a diverter valve to determine whether the heat should go to heating up hot water or heating up radiators. It fails and the heat goes the wrong way. That's why his brother has to turn his central heating on when he wants to have a shower.
He says the heat exchanger that allows the heat to come from the burner to the hot water does tend to fill up with limescale in hard water areas. This limits the amount of heat it can produce, so that's another possibility. They are usually a relatively simple part to change.
It would be good to know if the boiler is kicking in, ie slowly turn the hot tap on and check that with a moderate flow the boiler clicks in and starts working.
He says that the length of pipe will not really make a lot of difference unless it is several houses away. Within 20 seconds hot water should get anywhere. It's more likely the water is not leaving the boiler hot.
A good plumber should be able to fix it, but unfortunately there are a lot of average plumbers about.....

 

[Flyfisher]

So the boiler is heating 15 radiators well enough but not providing hot water to the taps? In which case, Zebra's suggestion about the diverter valve makes sense because it sounds like the boiler itself is functioning ok and can generate enough heat, it's just not getting into the right place.

If the boiler was 'furred up' (quite possible after 10 years), wouldn't it affect the heating as well? Plus it would be a gradual build up from new, but it was said the system has never really worked well. Faulty diverter valve for many years? Hmm.

 

[Me!]

I had a diverter valve that would progressively get more stiff every few years and then not operate correctly. There were two screws that held the motorised head onto the valve body, and it was a simple job to undo the screws, turn the valve from end to end a few times with a large pair of pliers to free it up, screw the motor back on, and then it would work again. Mine usually got stuck at the radiators-off end during the summer whereas yours sounds like it is sticking towards the radiators-on end, but other than that the symptoms sound the same, and it costs nothing to try this fix so it's worth a go.

 

[Zebra]

Is that a diverter valve inside a combi, Me!? Or one that's installed free-standing, as it were, in pipework? That's certainly interesting that you could free it up and put it back. I would certainly try that if it were the stand-alone type. Would that work for one that's inside a combi? I suppose so but I wouldn't know where to start looking for it.

 

[Poorprincess]

When I turn on the hot tap the boiler is quick to click in, lighting up hot water light.
The pipe from the boiler also got warm but there is no insulation on the pipe work. The pipe that is exposed runs along the inside of an outside wall. Could this be the problem? I think a lot of the pipe work is concealed so would be difficult to insulate now.
We did have an engineer out a couple of months back who mentioned changing a pipe going to the hear exchanger I think, to the current standard so I will ask him to change it over and double check what you have all mentioned I think.
Thank you all for your advice. I thank god we arnt on a water meter but I would love to get it cracked!

 

[Flyfisher]

I mentioned insulation earlier because I was thinking more about long(ish) pipe runs in a cold attic, i.e somewhere that the pipe might lose a lot of heat. But if the pipework is all within the heated areas of the house then I'd doubt there would be much heat lost - certainly not enough that it takes 20 mins before warm water arrives at the tap!

15 working radiators suggests to me that the boiler itself is not the problem. If it can heat 15 rads it should be able to easily heat one shower, so the question is why is all that heat not getting into the hot water pipes? Or if it is, then where is it being lost before it gets to the shower?

As previously mentioned, can you trace the hot water pipe from the shower back to the boiler, feeling the temperature at each accessible point while the hot water is running? The idea being to trace the heat flow along the pipework.

 

[Poorprincess]

I can't really trace the pipes all the way to bathroom. From boiler they enter a little area behind a false wall that's about two feet wide then, from what I remember go straight upstairs, from this point they are under original old floorboards I assume. How easy would these be to take up? I guess a plumber would trace the exact location with a detector would he?

 

[Poorprincess]

If over the weekend we make access to the enclosed area and feel the pipe work we can see as to if the hot water is lost at any point, can you tell me how at some point the pipe work would 'lose' the hot water?

 

[Flyfisher]

Not really, that's the mystery. But if the pipe is hot leaving the boiler but not at the shower or hot water tap (not for 20 minutes anyway) then something is wrong somewhere. Is the flow at the hot water tap or shower good?

 

[Lostgardensof]

Would you be able to borrow a thermal imaging camera from anyone? Might save you taking up floorboards.

 

[Owain]

Would you be able to borrow a thermal imaging camera from anyone? Might save you taking up floorboards.

Or a cat; it's a slow process but eventually you will be able to map the warmest parts of the floor -- and that will be where the heat loss from the pipe is greatest.

 

[Easrow]

Have you ever thought about it being the actual shower valve. My parents have a mira shower that every few years needs new o rings etc in the valve or they can't adjust temperature. Just a thought.

 

[fernicarry]

Was it converted from a gravity system (one with a hot water cylinder in a cupboard) to a combi (mains) system? I had this done in my flat and was left with really long pipe runs that took an age for hot water to come through. Well, 2 or 3 mins but that was a small flat. The hot water goes from the combi to where the tank used to be in the upstairs cupboard then back down again so travels about 4 times further than the straight line distance would suggest.

If its on 22mm pipework that also slows things down as it holds a lot more water than 15mm (more than twice a much). Gravity systems are usually on 22mm to get half decent flow rates (less resistance) but mains pressure DHW is generally fine on 15mm.

 

[Me!]

Is that a diverter valve inside a combi, Me!? Or one that's installed free-standing, as it were, in pipework? That's certainly interesting that you could free it up and put it back. I would certainly try that if it were the stand-alone type. Would that work for one that's inside a combi? I suppose so but I wouldn't know where to start looking for it.

Ah sorry, that was a free-standing one that I was referring to.