Hot water problem, combi boiler at fault?

[Gavin77]

Hello all, after a bit of advice.

My parents have just moved into a bungalow and there is something not right with the hot water. I didnt really have time to try and diagnose exactly what was going on but the basics are:-

Appear to get hot water from the kitchen tap (Close to combi boiler)
However in the bathroom the water never gets above luke-warm, but i noticed that the bathroom radiator got hot when running the tap.

The combi boiler is a baxi, and was apparently serviced a week before they bought the place.

I see two possible faults.
1. the diverter valve in the boiler (Would this have been checked as part of the service?)

2. There is some serious plumbing problem somewhere

Does (1) sound like the most likely culprit? Sorry i dont have more specific details, but was only there for a very short time.

Gavin

 

[ChrisOxford]

Hi Gavin,

Your suggestions are good ones.

It's a bit odd that the kitchen seems fine and the bathroom doesn't. It would be worth doing some more thorough checks.

Are your parents familiar with combis? If the bath is a long way from the boiler, opening the hot tap can often give cold->tepid->cold->hot water. It can take at least a minute for the water to become hot.

Also, having a bath tap open fully means that the flow rate through the boiler is very high, which leads to less heating and a lower hot water temperature.

On my combi, the bathroom rad gets warm after running a hot tap - it's a deliberate deisgn feature designed to cool down the main heat exchanger when the hot water demand stops.

 

[Agile]

A combi can only supply about 9 litres per minute of hot water.

Set the bath tap to that flow rate and see how it copes.

The rad should not normally get hot but some non combi systems are designed to heat a rad. Could easily be a historical aspect that was not corrected when the combi was fitted.

For the moment try turning off the rad and see if that makes any difference to the hot water.

You may well need to call a boiler engineer to identify the cause and suggest how to overcome it.

Kevindgas from this forum is in your area and has reasonable charges.

Tony

 

[bengasman]

Running the bathtap at half the max flow will probably sort the problem; this is often the case with cheap boilers/poor installs.

 

[Arthur2shedsJackson]

My Mother in law has a Combi, with very much the same problems as you describe.

You can't have taps fully open or you never get a good supply of hot water.

Basically they're great for central heating, but no good for hot water. May opinion is that they should be banned.

 

[bengasman]

...Basically they're great for central heating, but no good for hot water. May opinion is that they should be banned.

Maybe we should ban all boilers, you don't seem to be doing too well with non-combis either. At first, I thought it was a double post, but you just seem to have a problem with boilers in general.
Or maybe you just have problems.

I have a problem with the hot water being only tepid.
This is not a combi boiler.....

 

[Arthur2shedsJackson]

The boiler I now have a problem with has given us great service for the past 17 years and for the previous occupants for 3 years before that.

I expect to have some problems in that time and since this is the first time in all those years that we have had any problems with the water being anything but hot it's more than acceptable. It's not actually a boiler problem just something in the control system I think.

However my experiences with combis are that they are tempramental, don't provide what they are supposed to and don't cost that much less to run in the great scheme of things. In fact they are probably more expensive to run taking all the repair work they need into account.

I don't have a problem, and I don't have a problem with all boilers, but give me an open vented system any day!

By the way, have you got any constructive suggestions on my Open Vented system problem or are you just a Combi Lover?
Or worse still, are you the Ban All Sheds of the Plumbing Forum - Oh No !!!

 

[Gavin77]

Hi guys thanks for the replies.

My folks havent had a combi before but ive had them for years.

It is not simply warm up time. I left the tap running for 5 minutes. I also tried the tap half on, and it didnt seem to make any difference. (but maybe i didnt leave it long enough at 1/2 flow)

As for the rad, I understand that combis run the CH pump to cool the heat exchanger, but surely they shouldnt when actively drawing hot water? You could feel the radiator pipe getting hotter while the bath tap was open.

I'll probably be round there again at the weekend and hopefully will have more time to work out exactly what is going on.

Gavin

 

[xr4x4]

Is it possible that a heat exhanger has rusted through, allowing the domestic hot water through to the heating circuit?

Or something like that?

 

[mysteryman]

The diverter valve in the combi is letting by.

You can't slag all combis off because of one that needs some repair work. Combis are fine if you like them, as millions of people do.

As Agile Tony knows perfectly well, there are combis which can provide far more than 9 litres per minute.

 

[Arthur2shedsJackson]

. Combis are fine if you like them, as millions of people do.

.

In other words, they're an acquired taste !!

It's fair to say that millions of people have them, but I bet that a poll of those millions would reveal that a higher percentage would rather not have them.
They've been forced into them by the Environment Police.

 

[transam]

. Combis are fine if you like them, as millions of people do.

.

In other words, they're an acquired taste !!

It's fair to say that millions of people have them, but I bet that a poll of those millions would reveal that a higher percentage would rather not have them.
They've been forced into them by the Environment Police.

Probably more to do with install costs than enviromental concerns , in any event most combis ( all ?) could be used as systems boilers with a storage cylinder , if that is what customers want ?

 

[Arthur2shedsJackson]

That's true, but howmany of those people with combis actually know that?

 

[Gavin77]

OK thanks, I'll get them to have the diverter valve checked.

Now seeing as my thread has been hijacked...

My opinion on combi's, as with most things there are advantages and disadvantages.

I have a 28kW combi, and it gives loads of hot water.
+ Power shower without the pump
+ Always have hot water
+ Take less space (No tanks / cylinders - can be important in a small house.

- Long warm up period (throw 5 - 10 litres of water down the drain before it gets hot)
- No back-up for hot water if boiler fails.

i've sorted out the 1st disadvantage by fitting an instant electric heater at the kitchen tap outlet, which is fantastic (By the time you move your hand from the tap to the spout, the water is hot)

So all in all, for my small 3 bed house, the combi does a fantastic job and i don't see any advantage of having a conventional system. Obviously a bigger house, with multiple showers etc, then the combi isn't going to work very well. So, horses for courses...

 

[Arthur2shedsJackson]

Hi Gavin,
What's the cost of the instant hot water heaters and how much do they cost to run?

I assume that you completely disconnect the kitchen tap from the combi supplied system?