Large C/H system strugling to get hot.

[Bodd]

Hello All

I need some opinions before I tackle this job.
A customer of mine has a 2 year old heating system that they say has never got that hot. It consists of:

1 x Valiant eco tec plus 624 RI and
1 x Valiant eco tec plus 618 RI

They are situated in the converted loft serving 20 radiators and two 210 litre open vented cylinders.
The house is a large 3 floors (5 levels) 1920's style with a cellar.

Problem is after balancing I can only get 4 or 5 rads hot as you would expect maybe another 5 Ok'ish (but not exceptable) one that will not heat up and the rest that get luke warm.

I have put a balancing valves on the cylinders.

I'm not lost on this and have my ideas but would like some second opinions.

I have not done no calculations but recon the the boilers are up to he job a 28mm gas supply does go a long distance but all the way to the boilers.
the boiler flows do have a non return valve fitted on each, for some reason.

I could remove these but don't feel it will make much difference,

I could fit an additional 15-60 pump to help push around the system

I also get the feeling the pipe work could be undersized.
I have not investigated this in any great detail but can see 22mm is leaving the boilers via a 28mm manifold as such.

Each of the 3 floors are zoned with there own thermostat as well as the 2 cylinders.


I suppose there could be partial blockages.
The pressure was low on the gages so I had to top up.

I'm would love to get my teeth into this but also don't want to waist time on a job without a satifactorie outcome.


Hope I have not bored you.

Bodd

 

[glasgowgas]

brief scan of post only, first thoughts,

up pump to 25/80

15/60 no use for 42 kw

28mm gas supply goes a long way....how long? probably up it to 35mm

3 htg zones and 1 dhw zone....personally would have rigged up "like" a low loss header and seperate pumps

hope it helps

 

[Agile]

But the 624 and 618 are system boilers with their own built in pump.

Each has a pump which is adequate for its own heat output.

They seem to have been fitted in parallel hence a non-return valve is required.

I fear there is something else which is causing a poor flow around the heating circuit.

Tony

 

[kevindgas]

have a similar set up that we did a couple of years ago 438 and 428 side by side

the pump is a 25/80 feeding into the main set up, this consists of
1 heating zone with valve
1 UFH zone with valve and 15/60 grundfos Alpha pump
1 cylinder zone with valve ( 200 litre)
1 auto bypass

primary pump is controlled by 2 zone valves (1 on flow from each boiler) either will activate the pump
18 rads including 2 x 7' spiral towel rails

the boilers in your situation should cope happily with the demand unless the rads are huge.

 

[Biggles..]

sounds like a bad design.

should have been joined into a low loss with a primary pump. Boiler pumps should have been shunts.

I'd also suggest that you try balancing with the cylinders off, 2 x210 litre cylinders probably have high recovery coils of around 15KW each if they're cold and calling you wont balance jack.

gas sounds undersized but that wont be your problem.

 

[Bodd]

brief scan of post only, first thoughts,

up pump to 25/80

15/60 no use for 42 kw

28mm gas supply goes a long way....how long? probably up it to 35mm

3 htg zones and 1 dhw zone....personally would have rigged up "like" a low loss header and seperate pumps

hope it helps

Thank for reply. gas is a good distance and I will need to calculate to see if it could do with up sizing. I will fdo as you say for pump. Burt feel I have to work with what I have and getit workingthe best I can. These boilers never seem to take a breath and arer constanly fired up.

Bod

 

[Bodd]

But the 624 and 618 are system boilers with their own built in pump.

Each has a pump which is adequate for its own heat output.

They seem to have been fitted in parallel hence a non-return valve is required.

I fear there is something else which is causing a poor flow around the heating circuit.

Tony

I think these pumps are not man enough for the system but the boilers are. It is a big system, So do you think id still need the non return valves in if I fitted the new pump futhure up the flow beyound both boilers.

You mayb right about something else causing bad circulation and feel I may power flush the system but it is only 2 years old.

Bod

 

[Biggles..]

all cascaded boilers should have nrvs

try reading vaillants commercial pipe layout.

if adding a primary pump you need a low loss.

i take it both boilers share the combined load.

try this diagram for help sorry its a bad scan but notice the isolation valves and NRV's fitted at each boiler.

View media item 18024
Lee

 

[Terrywookfit]

Read post 5 again.

Have you done a gas rate check?

Too Late

 

[Bodd]

have a similar set up that we did a couple of years ago 438 and 428 side by side

the pump is a 25/80 feeding into the main set up, this consists of
1 heating zone with valve
1 UFH zone with valve and 15/60 grundfos Alpha pump
1 cylinder zone with valve ( 200 litre)
1 auto bypass

primary pump is controlled by 2 zone valves (1 on flow from each boiler) either will activate the pump
18 rads including 2 x 7' spiral towel rails

the boilers in your situation should cope happily with the demand unless the rads are huge.

The system has no Auto bypass so I think I should fit one while I'm fitting the pump.

At the moment the two boiler flows join into a combined 28mm flow that then reduces down to 22mm on each individual zone vavle supplying each floor and each cylinder, apart from the top floor, a 15 mm flow and return.


Rads are average size desighner rads with fancy lock sheild valves but no TRV's.

Bod

 

[Bodd]

Read post 5 again.

Have you done a gas rate check?

Too Late

No I have not. I think this is more a flow problem in the main. but do feel the gas supply to the boilers and the size of meter need to be investigated as well.

If the gas side was spot on I still don;t think it would solve the problem.

Bod

 

[Bodd]

all cascaded boilers should have nrvs

try reading vaillants commercial pipe layout.

if adding a primary pump you need a low loss.

i take it both boilers share the combined load.

try this diagram for help sorry its a bad scan but notice the isolation valves and NRV's fitted at each boiler.

View media item 18024
Lee

Thanks Lee

Just spoke to a mate who reckons I should maybe take these NRV's out and see what that does, what could the implecations be if I done just that.

Bod

 

[Bodd]

The reuturn back to boilers only really gets luke warm, yet on luke warm rads the the flow gets rather hot entering the rad.


How about installing a Alpha pump with a flow switch on the return back to the boilers.

Could installing a too powerful pump have a negative effect on the two existing pumps in the boilers?


Could the lock sheild valves be cheap and are restricting the flow?
(There is not one TRV on the system)

Maybe there is muck in the system from when it was first installed. It was part of a major renovation so the builders or even the plumber could have been careless. So maybe I should suggest a good power flush.


Oh I don't know.


I apprieciate all your advice so keep it coming.


Bod

 

[Biggles..]

Where do we start.

Have you ever installed boiler cascades/multiple boilers.if you have you'd know unequal sized boilers on a common will give you trouble.
Fitting a large pump will cause havoc with the boiler pumps and sensor.

Do not remove the NRV's they're there for protection

do read the drawing I posted,seriously consider altering to fit a LLH if your fitting a large pump.

Is the load actually sized per the boilers.

Have you took a water sample.

Have you calculated the resistance for your index to see if the boiler pumps are big enough

have you ensured boiler pumps are set to the correct speed

oh by the way if it's a large system your EV's are unfersized

 

[Bodd]

Where do we start.

Have you ever installed boiler cascades/multiple boilers.if you have you'd know unequal sized boilers on a common will give you trouble.
Fitting a large pump will cause havoc with the boiler pumps and sensor.

Do not remove the NRV's they're there for protection

do read the drawing I posted,seriously consider altering to fit a LLH if your fitting a large pump.

Is the load actually sized per the boilers.



Have you took a water sample.

Have you calculated the resistance for your index to see if the boiler pumps are big enough

have you ensured boiler pumps are set to the correct speed

oh by the way if it's a large system your EV's are unfersized

Sorry Lee can not really make out the Diagram
Never fitted that system.

Sorry to sound dumb but can't think what EV's are
or a LLH.

I take on bored what you say about a larger pump so how about I fit a 15/60 on the return side. The pumps on boilers are set so don't think I can alter them.

We do know how to spend a Christmas eve don't we.

Thanks Lee