Unvented cylinder not providing hot water to sinks,only showers

[rado16v]

Hi there,

hopefully someone can help figure out this issue we've been having for a few weeks now. The system is 13 years old and has been fine up until now, nothing has changed.

We have a unvented cylinder as per pics, all the sinks in the house (kitchen, utility, wc, en-suite and master bathroom) take an age for the water to get hot, when (if) it eventually does get hot it goes cold again and remains cold. The showers in the house are absolutely fine and remain hot.

In the pic, the pipe to the showers (marked) from the cylinder are always hot, they only feed the showers. The pipe at the top of the cylinder feeds all the sinks and this pipe will be hot at first if the hot water has not been run for a while but quickly goes cold when a tap is run.

It does sound like an airlock of sorts but wouldnt know where to start.

Appreicate your thoughts.

 

[stem]

Is it possible that the taps are supplied from somewhere else? For example direct from a combi boiler? What I mean by that is that the instantaneous hot water side of the boiler is only supplying the taps, and the unvented cylinder is supplying only the showers. So the same boiler provides the heat for both, but in two separate ways.

The fluctuating symptoms you describe are often associated with hot water produced directly from a combi.

 

[Johntheo5]

Hi there,

hopefully someone can help figure out this issue we've been having for a few weeks now. The system is 13 years old and has been fine up until now, nothing has changed.

We have a unvented cylinder as per pics, all the sinks in the house (kitchen, utility, wc, en-suite and master bathroom) take an age for the water to get hot, when (if) it eventually does get hot it goes cold again and remains cold. The showers in the house are absolutely fine and remain hot.

In the pic, the pipe to the showers (marked) from the cylinder are always hot, they only feed the showers. The pipe at the top of the cylinder feeds all the sinks and this pipe will be hot at first if the hot water has not been run for a while but quickly goes cold when a tap is run.

It does sound like an airlock of sorts but wouldnt know where to start.

Appreicate your thoughts.

Why are the HW take offs from two places??, one would think that the top one (sinks) should stay hotter longer than the shower (lower) take off as the cold water rises up through the cylinder on HW draw off.

 

[oldbuffer]

One possibility worth investigating is to see if there is a secondary circulation pump. Such pumps are used to ensure hot water circulates all the time so that turning on a hot outlet results in (almost) immediate hot water flow.
Such a system requires a special pump (bronze of stainless steel) and is often time controlled to avoid running when there is little call for hot water (e.g. overnight). If the pump is faulty, or has been switched off, it might cause the symptoms described. It would also explain the two hot connections. The one coming off the top of the cylinder is the normal one to all hot outlets. The lower one (just above the tun dish) could be the return for secondary circulation.

 

[rado16v]

Is it possible that the taps are supplied from somewhere else? For example direct from a combi boiler? What I mean by that is that the instantaneous hot water side of the boiler is only supplying the taps, and the unvented cylinder is supplying only the showers. So the same boiler provides the heat for both, but in two separate ways.

The fluctuating symptoms you describe are often associated with hot water produced directly from a combi.

Hi, no the hot water for the sinks is definitively coming from that pipe at the top as I can feel the water rushing through.

 

[rado16v]

Why are the HW take offs from two places??, one would think that the top one (sinks) should stay hotter longer than the shower (lower) take off as the cold water rises up through the cylinder on HW draw off.

No idea, was fitted that way from the beginning. I recall the heating engineer saying he had separated the showers from everything else as it was beneficial, I can't recall why now.

 

[rado16v]

One possibility worth investigating is to see if there is a secondary circulation pump. Such pumps are used to ensure hot water circulates all the time so that turning on a hot outlet results in (almost) immediate hot water flow.
Such a system requires a special pump (bronze of stainless steel) and is often time controlled to avoid running when there is little call for hot water (e.g. overnight). If the pump is faulty, or has been switched off, it might cause the symptoms described. It would also explain the two hot connections. The one coming off the top of the cylinder is the normal one to all hot outlets. The lower one (just above the tun dish) could be the return for secondary circulation.

Did look for one but there are no signs of it, cheers.

 

[Johntheo5]

Yes, the shower HW take off actually is from the HOT RETURN, its stamped on it, below where you have written showers. You say the taps run cold after running hot after awhile. Is the top pipe still very hot a few feet along from the top?, just wondering if you have a mixing problem somewhere on the taps system.

 

[rado16v]

Yes, the shower HW take off actually is from the HOT RETURN, its stamped on it, below where you have written showers. You say the taps run cold after running hot after awhile. Is the top pipe still very hot a few feet along from the top?, just wondering if you have a mixing problem somewhere on the taps system.

As the top pipe comes out it starts hot and is hot if you follow it along but then cools down and becomes cold as you head back so as if cold water is being pushed into the cylinder.

I noticed this with the pipe to downstairs WC which is the nearest to the cylinder. I isolated the hot water feed to this and it's definitely made things better, the kitchen tap is hotter and stays hot longer but it does cool down, but still hot. Upstairs, they stay cold however.

A mixer problem sounds plausible now, on the weekend, I'll isolate all the taps one by one and see if I can track it down to more than 1 dodgy tap.

I'll keep you posted.

Cheers

 

[Johntheo5]

Is the cold supply taken off a (the) balanced cold after the PRV cold to the UV cylinder? or is it supplied from another separate PRV or maybe its direct from the mains.

 

[DP]

Run a cold tap in the bathtub, then while cold tap is running try hot tap and see if you are getting hot water

 

[Johntheo5]

As the top pipe comes out it starts hot and is hot if you follow it along but then cools down and becomes cold as you head back so as if cold water is being pushed into the cylinder.

I noticed this with the pipe to downstairs WC which is the nearest to the cylinder. I isolated the hot water feed to this and it's definitely made things better, the kitchen tap is hotter and stays hot longer but it does cool down, but still hot. Upstairs, they stay cold however.

A mixer problem sounds plausible now, on the weekend, I'll isolate all the taps one by one and see if I can track it down to more than 1 dodgy tap.

I'll keep you posted.

Cheers

Any update on the problem??

 

[rado16v]

Hi , I was just about to post an update.

I've tracked the problem down to 2 faulty mixer taps (both Hansgrohe PuraVida of same vintage).

I've isolated the hot water on those and we're back in service, will look to replace them in due course.

Thanks all for your help.

 

[rado16v]

So after 3 months the issue has reappeared. The hot water to the sinks fluctuates from hot to cold.

I still haven't replaced the 2 faulty taps (I know!) but the hot water was isolated. Thinking another tap elsewhere had the same issue I went around the house isolating all the sinks, both hot and cold this time. Now only the kitchen sink hot water remains, the cold is also isolated and it still fluctuates in temperature.

However, this time the pipe at the top of the cylinder to the sinks remains piping hot.

Any pointers at this stage?

Thanks in advance.

 

[Johntheo5]

From (my) post #10

"Is the cold supply taken off a (the) balanced cold after the PRV cold to the UV cylinder? or is it supplied from another separate PRV or maybe its direct from the mains."