Poor heat output from radiators

[srowe]

I'm looking for some advice of the possible reason for why my central heating rads don't really seem to get hot. I've a theory but I'd like someone more knowledgeable to comment.

We have a Vailant Ecomax 625E boiler, the system is quite large: 22 radiators (some doubles) split 11 ground floor, 11 first floor. It was installed about 11 years ago by a professional heating company.

The symptoms are as follows, while the flow pipe for the rads gets very hot the return is barely lukewarm. I've attempted to balance the radiators (12C difference between flow and return) but it became impossible after the first half dozen as the difference was always higher. In fact the radiators at the far end of the circuit have their LSV and thermostatic valve fully open and they're only lukewarm when the system has been on all day.

The boiler has a modulating pump, I've tried adjusting the output but it didn't seem to make a noticeable difference.

The hot water is heated without any issue.

My suspicions are that the water is preferring to circulate around the hot water circuit rather than the rads. In the airing cupboard there is a bypass pipe before the servo with a pressure relief valve. The body of this value is constantly very hot, even when both the hot water and central heating servos are open. I've tried adjusting the valve, it has numbers from 1 to 6, but that makes no difference.

I'd order and replace this valve but as they're 50 quid I want to know that I'm on the right track first. I'm happy to pay for a professional to fix this but I have problems finding someone reliable and that actually answers their phone to make an appointment.

This has been rather a long first post, thanks for reading this far.

Simon

 

[Last Plumber]

I'd advise you to get a heating engineer in.
The pump is in the boiler so you should be Gas Safe registered to work on it ( gas appliance)
The cylinder is unvented ( you mentioned pressure relief valve), and needs an engineer qualified for the G3 regulation.

Sorry I can't be of more help.

As far as your issue goes, it could be a number of things

 

[Scott_D]

Any different with heating on and hot water off?

 

[srowe]

Any different with heating on and hot water off?

I've run that the last couple of weekends all day, rads still lukewarm and the bypass hot.

 

[ShaunCorbs]

Could be a few things

Sludge in the rads
Port valve passing on hot water

Any chance of a few pics of the bypass valve ?

 

[srowe]

Could be a few things

Sludge in the rads
Port valve passing on hot water

Any chance of a few pics of the bypass valve ?

I tried to link to the bypass valve but the site won't let me. It appears to be "RS Pro Pressure Relief Valve, 3/4in, 3bar" part number 246-3289 according to the RS web page.

A week or so ago I shut down the thermostatic valves on 6-8 of the rads and the ones are the end of the circuit got nicely hot.

 

[srowe]

Could be a few things

Sludge in the rads
Port valve passing on hot water

Any chance of a few pics of the bypass valve ?

I tried to link to the bypass valve but the site won't let me. It appears to be "RS Pro Pressure Relief Valve, 3/4in, 3bar" part number 246-3289 according to the RS web page.

A week or so ago I shut down the thermostatic valves on 6-8 of the rads and the ones are the end of the circuit got nicely hot.

 

[ShaunCorbs]

Bypass valve

http://m.ebay.co.uk/itm/Honeywell-A...%3Ac1473d5f1590a5e0b6f0ce29ffb06c65%7Ciid%3A1

But could be pump/balancing issue as well depending on age could be warn best get a gas safe engy to have a look

 

[srowe]

Bypass valve

...

But could be pump/balancing issue as well depending on age could be warn best get a gas safe engy to have a look

Thanks, I'll keep trying to locate a engineer, the boiler needs an annual service.

Out of interest, it is usual for these valves to fail? The one on the hot water tank had to be replaced a couple of years ago.

 

[srowe]

Bypass valve

...

But could be pump/balancing issue as well depending on age could be warn best get a gas safe engy to have a look

Thanks, I'll keep trying to locate a engineer, the boiler needs an annual service.

Out of interest, it is usual for these valves to fail? The one on the hot water tank had to be replaced a couple of years ago.

 

[quality]

everything fails when its not looked after and serviced

 

[king of pipes]

Has it ever worked properly ? could be undersized pump or Kw output of boiler 22rads and a cylinder bit small i would say

 

[ShaunCorbs]

may i ask whats with the cloth around the immersion heater?

 

[srowe]

Has it ever worked properly ? could be undersized pump or Kw output of boiler 22rads and a cylinder bit small i would say

No, they've really never been great. The boiler is rated are 35kW. I'm not sure what specifications are relevant regards the pump, there's a graph which shows up to 1900 l/h.

 

[king of pipes]

Lack of maintenance

 

[srowe]

may i ask whats with the cloth around the immersion heater?

There's a sorry tale. There was some weeping around the immersion heater, I had a plumber in a couple of years ago to replace it, he took hours to do it and when he finished it was still the same. "Will probably clear up over time", still leaks.

 

[srowe]

may i ask whats with the cloth around the immersion heater?

There's a sorry tale. There was some weeping around the immersion heater, I had a plumber in a couple of years ago to replace it, he took hours to do it and when he finished it was still the same. "Will probably clear up over time", still leaks.

 

[srowe]

Lack of maintenance

The system has been serviced by professionals every year for the past seven years.

 

[srowe]

Lack of maintenance

The system has been serviced by professionals every year for the past seven years.

 

[ShaunCorbs]

No, they've really never been great. The boiler is rated are 35kW. I'm not sure what specifications are relevant regards the pump, there's a graph which shows up to 1900 l/h.

are you sure normally vaillant on the last two numbers on the model is the kw

 

[srowe]

are you sure normally vaillant on the last two numbers on the model is the kw

It's an ecoMAX 635E, I had a typo in the initial post.

 

[king of pipes]

Is that a system boiler meaning pump inside the boiler casing ? output on that boiler is 34.9kw flat out 22 rads say 2kw each some more some less 44 kw + undersized low loss header with a bigger pump Dab Evosta 40 -70 7 metre pump should do it get the professionals back and get em to sort the emersion heater leak out not that hard to do .

 

[Sparkgap]

No, they've really never been great. The boiler is rated are 35kW. I'm not sure what specifications are relevant regards the pump, there's a graph which shows up to 1900 l/h.

Sounds like it could be the bypass letting by (is there a means of shutting it off to check?). I'd also be wary about using the boiler pump for the whole system, but not knowing the layout couldn't give a definitive answer. Most system boiler internal pumps don't have a particularly high head (I think the Vaillant is about 2.5m) and you might find your system is higher resistance, hence not getting the flow to distant rads.
Another thing: doesn't the Vaillant have an internal bypass fitted? If that's letting by there will be less head available.
Assuming it's lack of oomph from the boiler pump you might need to put in a low loss header with a larger pump on the system side.

 

[srowe]

Thanks for all the feedback. I've got someone booked to service the boiler next week, I'll talk this over with them when they're here.

 

[srowe]

Another thing: doesn't the Vaillant have an internal bypass fitted? If that's letting by there will be less head available.

I've just looked at the manual, yes

3.12.2 System by–pass
An automatic system by–pass is included within the boi-
ler. The boiler is suitable for use in systems with ther-
mostatic radiator valves and no additional by–pass is
required.

Is it usual to also fit an external bypass, or could this be the source of the problem?

 

[king of pipes]

No its not unsual its let's the boilers pump still have a circuit should the rad TRVS close or get turned off when the boiler reaches its set tempreture and switches off the pump continues to run to reduce the tempreture in the heat exchanger the bypass in the boiler is only a small pipe so not so good works better having a external one fitted , you could try replacing it or even better move it near the boiler personally I would still say your boiler is undersized .

 

[Stigster]

Why is a 3 bar pressure relief valve being used as a bypass, if that is what it is in your picture?

Edit - I see that it is a bypass valve. Haven't seen that type used round my way before.

 

[ShaunCorbs]

Why is a 3 bar pressure relief valve being used as a bypass, if that is what it is in your picture?

Edit - I see that it is a bypass valve. Haven't seen that type used round my way before.

honeywell bypass mate

 

[srowe]

So I've just had an engineer out to service the boiler and talk about the issues I'm having. His opinion is that there is a flow problem and the system needs a power flush. It may also need an additional pump on the return given the size of the system but that should be reassessed after the system has been cleaned out.