New Viessmann - Hot Water Takes Ages

[Toki]

I got a new combi boiler, Viessmann Vitodens 100 fitted at the end of October this year. The hot water takes around 75 seconds to reach a hot temperature in the kitchen.

The boiler is installed in a garage, which is directly joined on to the house and is fitted behind the kitchen wall. The pipes run upstairs to the airing cupboard, where the hot water tank used to be, and then back downstairs to the kitchen. However, this isn’t the main cause I don’t think.

The boiler is set on Eco mode and takes a minute or more to heat up to 60 degrees C, starting from around the 30 degrees C mark according to the reading on the boiler. Is this normal? It seems to start off slowly, before cranking up volume and coming on full.

Thanks in advance for your help. If you need more info then let me know.

 

[muggles]

Remember also that the incoming mains is colder at this time of year, and that things won't be helped by your boiler being in an unheated space. It also sounds to me suspiciously like your installer has simply linked the hot supply to the old cylinder outlet, which is rather lazy and means that at some point the 15mm outlet from the boiler is running into a 22mm pipe full of cold water, the mixing effect of this will slow things down considerably. Ideally all 22mm hot pipework should have been removed and replaced with 15mm during installation.

 

[Agile]

I expect that the installer, possibly with your agreement or even instructions, reused 22mm hot water pipes for the hot water.

Mains fed hot water pipes are normally adequate at 15mm.
i 22 have been used, particulately when not insulated, then a lot of cold water has to be shifted before the water at the sink will be hot.

At the end of your cycle further heat is wasted when the water and pipes cool down.

A better way to pipe hot water is in insulated 15mm pipe direct from the boiler to the kitchen and seperately direct to the bathroom.

Tony

 

[Toki]

That is normal, and it is why Viessmann offer the Comfort mode. This keeps the plate heat exchanger hot when the timer calls for it. You will then get hot water from the boiler immediately - it may still go all around the house, but it will be quick from the boiler.

Thanks mysteryman, does the Comfort mode use a lot more gas then?

 

[Toki]

Remember also that the incoming mains is colder at this time of year, and that things won't be helped by your boiler being in an unheated space. It also sounds to me suspiciously like your installer has simply linked the hot supply to the old cylinder outlet, which is rather lazy and means that at some point the 15mm outlet from the boiler is running into a 22mm pipe full of cold water, the mixing effect of this will slow things down considerably. Ideally all 22mm hot pipework should have been removed and replaced with 15mm during installation.

Thanks muggles and agile, I suspect you may both be right. I'll check when I go home. I was never asked about changing the existing pipework out and never saw him removing pipework from the kitchen.

Would it be a big job to do now that the boiler is fitted? If this is the case, should I ask the installer back to do this free of charge? Is it normal to change the pipework?

Thanks again.

 

[Gasman77]

FOC!! haha !! I should think he'll laugh at you buddy. I would.

What would you have said if he told you he wanted to lift up loads of floorboards and carpets to reduce the size of your hw pipe and charge you a few extra quid for doing it, so it gets to your taps 20 seconds quicker? be honest.

And the rest of you should be ahshamed, pulling the RGI's work to bits on something so minor. Easy to be an armchair critic.

 

[mysteryman]

The Comfort mode will obviously use a bit more gas, but not significantly so.

I don't think you can expect your man to change your pipework FOC, although I always did change as much as possible to 15mm when I was installing.

 

[Toki]

Checked the pipes, the DHW and the cold water pipes going in to (and out of) the boiler are 15mm, also checked the pipes under the kitchen sink and in the bathroom and they are also 15mm.

The house was only built in 1992, I take it they would have been fitting 15mm pipes back then?

For reference, the pipes for the heating are 22mm.

I'll try the comfort setting tomorrow and see how much difference that makes. It does seem to take around a minute for the LCD display to reach 60 degrees, probably due to the really cold water that's coming in due to the weather here in Aberdeen!

 

[Gasman77]

I'd gas rate it if I were you, its something you can Diy and it will ensure you got plenty of gas at the boiler, just google it and you'll find out how to do it!

 

[ChrisR]

You can see from a post in the FAQ /Wiki section how to read a gas meter, worth checking.
The 15mm pipes which you mention , would all be 15mm, it's the ones near where the old cylinder would have been that may well not be. 22m holds about double the amount per metre that 15mm does, so a couple of metres won't be significant, but 10 would.

 

[Toki]

You can see from a post in the FAQ /Wiki section how to read a gas meter, worth checking.
The 15mm pipes which you mention , would all be 15mm, it's the ones near where the old cylinder would have been that may well not be. 22m holds about double the amount per metre that 15mm does, so a couple of metres won't be significant, but 10 would.

You are right Chris, there is a 22mm pipe in the airing cupboard where the hot water cylinder used to be. It goes under the floor so no idea how long the pipe is before it goes back to 15mm to the taps.

Cheers.

 

[Agile]

FOC!! haha !! I should think he'll laugh at you buddy. I would.

And the rest of you should be ahshamed, pulling the RGI's work to bits on something so minor. Easy to be an armchair critic.

Sounds like the thoughts of a cowboy plumber. Must be one of these time served people who learns early on how to cut corners to do a less than perfect job.

I would always explain whats involved to the customer and quote accordingly. Then the customer can decide.

Depending on the pipe route it can be quite involved, maybe £200, and could involve destroying decorations or floor coverings.

I always take the view that all jobs should be done in the best possible way. But then the customers are usually partly to blame for choosing the cheapest quote regardless of the quality of the design.

Its a lose lose situation for me. Even if I went and gave a free quote visit and advised the owner of what SHOULD be done then all he would do is take advantage of my free advice and get a cheap installer, probably unregistered, to do the job instead. Thats why I dont visit free to give quotes, but I do ask questions on the phone and give a budgetary price.

Tony

 

[Gasman77]

Keep up the advertising efforts Tiger, your so transparent its unreal. Like I said, there is the perfect Tony world, and then the real world which I think you dropped out of some time ago.

Gimp.

 

[Toki]

Following on from my earlier post, I've been living with the 60-75 seconds the hot water takes to come through.

I've noticed that if I turn the tap on and run hot water through for a bit, then turn it off for 30 seconds or so, then turn it back on, I get hot water to begin with which will already be in the pipe, then cold as the boiler fires up, and takes another 60-75 seconds.

Does the heat exchanger not stay warm for any length of time or does ths indicate a fault?

I would have thought hot water would take less time if the boiler had just switched off?

Thanks in advance.

 

[Toki]

Set the boiler in 'Comfort' mode, and you will have hot water at the boiler immediately. The rest of the delay is not caused by the boiler. If you have either a plug-in timer, or a Vi programmable room thermostat with plug-in base station, you can time the preheat on channel 2 of the timer.

Don't do the on-off trick, you are going back to the beginning of a water heating cycle each time you turn the hot tap on.

I've now have the boiler in Comfort mode but the same happens. The temp showing on the boiler starts around 30 degrees C when hot water hasn't been on for a bit, then boiler comes on slowly to begin with and heats up to around 60 degrees C after 60-75 seconds.

Are you saying it's quite normal for the whole cycle to start again then? For example, when doing the dishes, I fill the basin, turn tap off, then on during doing the dishes to rinse over plates and pans to take the worst off. It's annoying that the water gets cold again for over a minute. Is this quite normal?

When I turn the hot water on again after being off for >30 seconds, the boiler starts up slowly again. The temp then drops from the 60+ degrees showing on the boiler down to 40 degrees or so, then begins to rise before reaching around 60 after 60+ seconds. Correct me if I'm wrong, but I would have thought that it would retain some of the heat?

I have a Honeywell CM927 for the central heating, no option for hot water unfortunately.