UK Combi Boiler water to hot.

[mememe]

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

 

[telectrix]

faulty stat on boiler?

 

[Megawatt]

faulty stat on boiler?

I agree with telectrix that it sounds like you have a faulty thermostat

 

[odawire]

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.

 

[mememe]

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]

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 ?

 

[odawire]

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]

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

 

[mememe]

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.

 

[odawire]

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.
[automerge]1568485750[/automerge]

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]

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

 

[odawire]

That’s good money I’m like you I wished I got that kind of money good luck

Try living in London ?

 

[Megawatt]

Try living in London ?

No way my friend way to crowed for and no parking is what I hear

 

[Simon47]

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.

 

[mememe]

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