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Hi all, I have a combi boiler when I set the hot water at 60c on the boiler it goes right up to 70c when I run the shower after a few mins, should it do this or have I got an fault in the boiler.
the shower is the bar mixer type.
Can any one help. Thanks
 
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Most combi boilers dont have thermostats to control the heat of the water, its controlled through the flow of water through the heat exchanger.

Does it go up in temp for a bit then drop down and keep cycling like that? If so it is a blocked plate heat exchanger.
 
  • Thread Starter Thread Starter
  • #5
Most combi boilers dont have thermostats to control the heat of the water, its controlled through the flow of water through the heat exchanger.

Does it go up in temp for a bit then drop down and keep cycling like that? If so it is a blocked plate heat exchanger.
Hi thanks for your reply, no its not doing that, It starts off from 50c then slowly goes up when the shower is used till it reaches approx. 70c+
 

Megawatt

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Arms
Most combi boilers dont have thermostats to control the heat of the water, its controlled through the flow of water through the heat exchanger.

Does it go up in temp for a bit then drop down and keep cycling like that? If so it is a blocked plate heat exchanger.
On your heat exchanger do y’all have temperature transmitters on the inlet of the heat exchanger and on the outlet ?
 
On your heat exchanger do y’all have temperature transmitters on the inlet of the heat exchanger and on the outlet ?
Do you mean the main heat exchanger or the hot water one? Theres definitely sensors but they don't necessarily control the temperature, just for overheat.
 

Megawatt

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Arms
Do you mean the main heat exchanger or the hot water one? Theres definitely sensors but they don't necessarily control the temperature, just for overheat.
The heat exchanger and the transmitters which monitors the incoming temperature to the out going temperature which would tell me if I had a rise in temperature
 
  • Thread Starter Thread Starter
  • #9
On your heat exchanger do y’all have temperature transmitters on the inlet of the heat exchanger and on the outlet ?
Hi thanks , I did renew a thirstier or DHW Temperature sensor fitted to the heat exchanger, I had to do this as we error code come up & had no hot water, but this seems to be ok now, that was about 6 moths ago.
Some one said it may be the Hall effect sensor. Not to sure where that is?
I may have to get a local engineer out to check it all out.
But they quoted £90 hour, wish I got that when I was working.
Any way thanks for looking & your advice.
 
The heat exchanger and the transmitters which monitors the incoming temperature to the out going temperature which would tell me if I had a rise in temperature
On the main exchanger there are definitely in and out sensors. They control the main circulation. On the plate there are similar sensors. they will give a raise in temperature figure which you can check between the mains water and hot water to check it is working correctly.
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Hi thanks , I did renew a thirstier or DHW Temperature sensor fitted to the heat exchanger, I had to do this as we error code come up & had no hot water, but this seems to be ok now, that was about 6 moths ago.
Some one said it may be the Hall effect sensor. Not to sure where that is?
I may have to get a local engineer out to check it all out.
But they quoted £90 hour, wish I got that when I was working.
Any way thanks for looking & your advice.
Yea, you would be better of on the plumbing forum an
Hi thanks , I did renew a thirstier or DHW Temperature sensor fitted to the heat exchanger, I had to do this as we error code come up & had no hot water, but this seems to be ok now, that was about 6 moths ago.
Some one said it may be the Hall effect sensor. Not to sure where that is?
I may have to get a local engineer out to check it all out.
But they quoted £90 hour, wish I got that when I was working.
Any way thanks for looking & your advice.
Yea, you would be better off on the plumbing forum.
 

Megawatt

-
Arms
Hi thanks , I did renew a thirstier or DHW Temperature sensor fitted to the heat exchanger, I had to do this as we error code come up & had no hot water, but this seems to be ok now, that was about 6 moths ago.
Some one said it may be the Hall effect sensor. Not to sure where that is?
I may have to get a local engineer out to check it all out.
But they quoted £90 hour, wish I got that when I was working.
Any way thanks for looking & your advice.
That’s good money I’m like you I wished I got that kind of money good luck
 

Simon47

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Arms
Esteemed
It's "normal".
A combi has a minmum power input, which for a water efficient shower may be too high for the flow rate. So you start the shower, and at first it calls for a lot of hot water. As the hot water gets to the shower, the thermostat reduces the hot water flow rate - and the boiler will reduce the gas flow accordingly.
But it sounds like the shower is reducing the hot water flow rate beyond the point where the boiler can reduce the gas flow rate any further. At this point, the water temperature will increase.
What happens next depends on a number of factors. The shower temperature may creep up a bit and the system settle in a state where it's using as much heat as the boiler can range down to. The boiler outlet temperature may creep up to the point where the boiler turns off - at which point the hot water temperature will drop failure quickly before the boiler fires again.
Or, as we think happened to mother the other day, the shower valve may throttle down the hot water to the point where the boiler turns off. It will then stay off until cooler water reaches the shower valve and the stat starts calling for more hot water. The boiler will fire up again, but by now the boiler and pipe to the shower will have cold water in them and the shower will go cold for a while while the boiler gets warmed up and the hot water comes through the pipe.

Just one of "quite a few" reasons why I "strongly dislike" combi boilers.
 
  • Thread Starter Thread Starter
  • #15
It's "normal".
A combi has a minmum power input, which for a water efficient shower may be too high for the flow rate. So you start the shower, and at first it calls for a lot of hot water. As the hot water gets to the shower, the thermostat reduces the hot water flow rate - and the boiler will reduce the gas flow accordingly.
But it sounds like the shower is reducing the hot water flow rate beyond the point where the boiler can reduce the gas flow rate any further. At this point, the water temperature will increase.
What happens next depends on a number of factors. The shower temperature may creep up a bit and the system settle in a state where it's using as much heat as the boiler can range down to. The boiler outlet temperature may creep up to the point where the boiler turns off - at which point the hot water temperature will drop failure quickly before the boiler fires again.
Or, as we think happened to mother the other day, the shower valve may throttle down the hot water to the point where the boiler turns off. It will then stay off until cooler water reaches the shower valve and the stat starts calling for more hot water. The boiler will fire up again, but by now the boiler and pipe to the shower will have cold water in them and the shower will go cold for a while while the boiler gets warmed up and the hot water comes through the pipe.

Just one of "quite a few" reasons why I "strongly dislike" combi boilers.
Thank you for your reply, I do agree combo boilers are not good for showers. Before we had electric shower, I really do wish I put electric back in, It might come to that later.
again thanks
 

Megawatt

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Arms
Thank you for your reply, I do agree combo boilers are not good for showers. Before we had electric shower, I really do wish I put electric back in, It might come to that later.
again thanks
Do y’all not have plain old hot water heaters with thermostats. Boilers sounds dangerous
 
Thank you for your reply, I do agree combo boilers are not good for showers. Before we had electric shower, I really do wish I put electric back in, It might come to that later.
again thanks
Hang on... hang on... there's only 1 thing that Combi Boilers are any good at... and that's a decent shower !! You can shower as long as you want without any risk of running out of hot water... great for showering with a friend !

You just need to install and use correctly.

Electric showers usually give a woeful flow rate, especially in the winter when the incoming mains water is close to freezing !
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Do y’all not have plain old hot water heaters with thermostats. Boilers sounds dangerous
We have all sorts of methods to heat water here... the modern trend is to move away from a stored cold water supply, so usually we run off the water main. As for heating the water... the price of natural gas here (most households have access to it) is about ⅓ that of electricity so it's the popular choice... which usually means a combination gas boiler.
 
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Simon47

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Arms
Esteemed
I think the comment about "boilers" was a tongue in cheek way of pointing out that the one think we don't want them tobdo is boil.

No, combis are not great for showers. Before combis, thermostatic shower valves were something of a luxury - with a combi they're essential. The only thing in favour of combis is that plumbers don't have to think and developers can shave a square yard off the size of the shoeboxes.
For mains pressure hot water with endless supply and reliability - get a thermal store with passive DHW coil.
 
I think the comment about "boilers" was a tongue in cheek way of pointing out that the one think we don't want them tobdo is boil.

No, combis are not great for showers. Before combis, thermostatic shower valves were something of a luxury - with a combi they're essential. The only thing in favour of combis is that plumbers don't have to think and developers can shave a square yard off the size of the shoeboxes.
For mains pressure hot water with endless supply and reliability - get a thermal store with passive DHW coil.
I only said that showering was the best thing that a Combi did ! Personally, I hate the bloody things... and yes, you're right, easy to install and take up less space. Like you, if I had the space and it was my house... I'd go down the thermal store route, with solar and wood burning stove heat inputs... But we're now in the realms of a very very small number of houses.
 

davesparks

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Mentor
Arms
Esteemed
Do y’all not have plain old hot water heaters with thermostats. Boilers sounds dangerous
They are called boilers but they don't actually boil the water, a gas boiler typically heats water to around 70degrees C to be pumped around the heating system and to heat stored hot water.
I think this is another US/UK terminology confusion.
I believe you use something called a furnace in heating? To us the word furnace makes us think of big fires melting metals or other materials for industrial processes.

We have a couple of different standard methods of providing hot water to houses.

What systems do you use in the USA to provide hot water to houses?

In the UK the traditional method is to have an insulated copper tank to store a quantity of hot water, this can be heated directly by an immersion heater or indirectly.
Indirect heating is achieved by a long copper tube coiled inside the hot water tank, hot water from the boiler is circulated through this and heats the stored water.
Electric immersion heaters have a thermostat built in and indirect tanks have a thermostat linked to a motorised valve to shut off the flow of water from the boiler and switch off the boiler.

Another option is the combi boiler, this is like a standard boiler with a plate heat exchanger added to it. The heating water flows through one side of the plate heat exchanger and cold mains water is fed in to the other side. The cold mains water is heated in the heat exchanger to a temperature controlled by the boiler.
 

Simon47

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Arms
Esteemed
From watching stuff on telly, it seems that what we call an unvented cylinder with immersion heater is common in the US. Mythbusters did a bit on what happens if they explode...
They had to defeat all the safety features (thermostats, over pressure & over temp valves), but they managed it. The bottom seam failed and cylinder launched upwards, punching through a floor and roof of the skeleton house they'd put together :D
 

Megawatt

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Arms
From watching stuff on telly, it seems that what we call an unvented cylinder with immersion heater is common in the US. Mythbusters did a bit on what happens if they explode...
They had to defeat all the safety features (thermostats, over pressure & over temp valves), but they managed it. The bottom seam failed and cylinder launched upwards, punching through a floor and roof of the skeleton house they'd put together :D
Yes they can build up so much pressure it’s like a bomb but myth busters just showed what could happen after they defeated all the safety's such as the pressure relief valve and thermostat which would open when it gets to close to the pressure.
 

Simon47

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Arms
Esteemed
What do you call them over there ?
Over here it would generally be referred to as an unvented cylinder.
And yes, Mythbusters had to disable multiple safeties - thus demonstrating why we have the regs we do to make them safe.
 

Megawatt

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Arms
What do you call them over there ?
Over here it would generally be referred to as an unvented cylinder.
And yes, Mythbusters had to disable multiple safeties - thus demonstrating why we have the regs we do to make them safe.
Just a plain old hot water heater and mine is 50 gallons so we don’t run out of hot water
 

Simon47

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Arms
Esteemed
That would be confusing to us, as "hot water heater" could mean so many things ! We have instantaneous heaters, of which the gas (or oil) fired combi is one; vented cylinders (the traditional approach); unvented cylinders (needs all the safety stuff to be safe(ish)); thermal stores and heat banks; ...
And of course, each of the cylinders (or storage tanks) can be heated by different means, so that makes lots of permutations.
And head into the plumbing section of some forums, and you'll find supposedly professional plumbers state with pride how they'll never install (or recommend to a customer asking their advice) anything but a combi :rolleyes:
 

Megawatt

-
Arms
That would be confusing to us, as "hot water heater" could mean so many things ! We have instantaneous heaters, of which the gas (or oil) fired combi is one; vented cylinders (the traditional approach); unvented cylinders (needs all the safety stuff to be safe(ish)); thermal stores and heat banks; ...
And of course, each of the cylinders (or storage tanks) can be heated by different means, so that makes lots of permutations.
And head into the plumbing section of some forums, and you'll find supposedly professional plumbers state with pride how they'll never install (or recommend to a customer asking their advice) anything but a combi :rolleyes:
Hot water heater is just a phrase. You can call it what you want but it is electric or gas it has 2 heating elements in it with 1 thermostat for the top element and 1 thermostat for the bottom element and it has a setting on the first thermostat. It will go up to 140 degrees but I advise people to set it at 110 degrees Fahrenheit
 
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