Combi boiler - delayed hot water
Discussion
So I've always thought combi's were crap, but been looking after inlaws house and I'm astonished at how long it takes their Worcester 28CDi to produce hot water.
It gets there in the end, but takes a whole sinkfull of water for decent temp hot water to start coming through.
Looking at the design, on the face of it it's no wonder there's a delay. Hot water is produced through a water to water heat exchanger. So the boiler has to fire, heat up the water in the heat exchanger and then start exchanging heat with the incoming cold water.
Am I missing something here? Is there some setting on the boiler that needs changing (water temp was set in middle but didn't make any obvious difference when turned to max).
It gets there in the end, but takes a whole sinkfull of water for decent temp hot water to start coming through.
Looking at the design, on the face of it it's no wonder there's a delay. Hot water is produced through a water to water heat exchanger. So the boiler has to fire, heat up the water in the heat exchanger and then start exchanging heat with the incoming cold water.
Am I missing something here? Is there some setting on the boiler that needs changing (water temp was set in middle but didn't make any obvious difference when turned to max).
Mine can be running plenty hot enough within about 10 seconds tops. But then it is only 3 years old and the water only has to travel about 7 metres max from the boiler to any tap in the house
The one thing I have noticed is that the water is NEVER scorching even if you let it drip out, so we tend to run a bath slowly to get it very hot, but I can't say it has even been an issue.
All these downsides I can live with for the convenience on having hot water on tap as it were, and not having to organise myself half an hour before I want a bath or shower, and not paying to heat water that I don't need hot.
The one thing I have noticed is that the water is NEVER scorching even if you let it drip out, so we tend to run a bath slowly to get it very hot, but I can't say it has even been an issue.
All these downsides I can live with for the convenience on having hot water on tap as it were, and not having to organise myself half an hour before I want a bath or shower, and not paying to heat water that I don't need hot.
joewilliams said:
Mine can be switched between 'Comfort' and 'Economy'.
In comfort mode, it regularly fires up for 30 seconds to keep the boiler side of the heat exchanger warm.
Yes, I've seen that. Some also have a little store of hot water, so are pretty instant. However the model in the inlaws doesn't seem to have such features and in the summer (when not already in use for CH), it seems a heck of a long cycle time to hot water.In comfort mode, it regularly fires up for 30 seconds to keep the boiler side of the heat exchanger warm.
It is an issue with Combis, especially older types. My 12 year old Potterton takes maybe 30 secs to start producing usable hot water, only really an issue when washing up, I have to tip away half a bowl of cold water. For a bath I just run the hot and top up with cold to get the temperature right, bath takes 7 mins to fill, no big issue. My shower rocks!
Sorted in the new combis? I don't think so! Ours is brand new and we have a long wait for hot water. The old one (which was totally dire and British Gas were always around fixing) at least had a small inbuilt tank that was kept warm and therefore was a lot quicker. The new one doesn't so has said you have to wait for the heat exchanger to work and the hot water to then run through the system.
Equally no reduction in the amount of gas used between the old and new one either!
The old system of a boiler supplying a large well insulated hot water tank is definitely best, and of course means that in the event the water is off for any reason you have a supply of hot water in the tank, and cold water in the loft tank to use until it comes back on. With a combi you have no water tanks so no water the moment it goes off!
Equally no reduction in the amount of gas used between the old and new one either!
The old system of a boiler supplying a large well insulated hot water tank is definitely best, and of course means that in the event the water is off for any reason you have a supply of hot water in the tank, and cold water in the loft tank to use until it comes back on. With a combi you have no water tanks so no water the moment it goes off!
ive just recently swaped out my economy 7 system during my house build up, i went with a worscester bosch (sp) but i went with 42cdi , the top model and its gets very very hot quickly even in economy mode, my problem with this boiler isnt the time it takes to heat the water or the house for that matter but its the amount of gas it uses which is rather alarming to be honest.
Just to close this: The inlaws said they thought the boiler's performance had deteriorated so they called a Worcester Bosch serviceman.
He found "an unusual" problem with the diverter valve where it wasn't fully diverting so was trying to heat the rads at the same time as the internal water to water heat exchanger. He also changed that heat exchanger too.
It now performs perfectly adequately.
One thing I though was a bit odd is that the serviceman said the water flow was too high (so reducing the hot water temp) due to high mains pressure - I thought there was a device in the boiler to restrict the flow according to the boiler's rating?
He found "an unusual" problem with the diverter valve where it wasn't fully diverting so was trying to heat the rads at the same time as the internal water to water heat exchanger. He also changed that heat exchanger too.
It now performs perfectly adequately.
One thing I though was a bit odd is that the serviceman said the water flow was too high (so reducing the hot water temp) due to high mains pressure - I thought there was a device in the boiler to restrict the flow according to the boiler's rating?
In germany we don't have any tanks (ironically enough 
) cold or hot
we have a thing like an electric power shower in the bathroom (no, not gas showers), connected to the bath taps and shower - very hot, good pressure
then a similar smaller one in the kitchen, that one does have a built in little tank, about 5 litres - scorchio hot
) cold or hotwe have a thing like an electric power shower in the bathroom (no, not gas showers), connected to the bath taps and shower - very hot, good pressure
then a similar smaller one in the kitchen, that one does have a built in little tank, about 5 litres - scorchio hot
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