Suspect pump?

[Rover05]

Hi all,

Recently moved into a house with a newish boiler - ideal classic HE. Unfortunately the pipework is all 8mm microbore.
So I've power flushed the system and refilled with mainly distilled (hard water area) and fernox.

Other than regular rad bleeding - as with all drained and flushed jobs, the system has been good.
However, two months in and with the cold weather I find the boiler regularly trips out on high temp. I suspect the pump (Grundfos) is not providing the required throughput or maybe the boiler is airlocked or coked?
Any advice appreciated.

 

[gas4you]

Have you set the pump to its fastest setting eg 3?

Do you have an auto bypass fitted after the pump?

With microbore I would usually expect it to need a pump on full, especially if it is all 8mm.

 

[Agile]

8 MM gives a considerable flow resistance and may well be inadequate for the boiler if there is no auto bypass fitted ( as there should be! )

If your pump is a 15-50 then it might help a little if it was upgraded to a 15-60 which has a slightly higher head pressure.

Tony

 

[Rover05]

Hi guys,

Re the bypass - there is a manual hand valve.I now have it completely shut, hopefully forcing as much round the system as possible.

Re the pump, it is a Grundfos 15-60. It gets very hot. When the bleed screw is removed from the centre - should water literally p*ss out or are the fins sealing that tight it just drips out - which is what it does?

As I say, I don't know whether the pump is poor or it is a boiler problem?
Cheers.

PS the boiler burner is literally red hot !

 

[gas4you]

Water should be a continuous trickle from the pump when the center screw is removed.

 

[Rover05]

Cheers gas4you,

Grundfos is on position 3 too. Don't know whether to take a punt and replace pump or just get BG around to look at the boiler. I'm pretty handy but draw the line at boilers!!!!

 

[Agile]

BG will not be able to better the advice that Dave and I have given you!

Your problem is just that its 8 mm ( as long as thats clean and not blocked! ).

You should never have had a gate valve as a bypass! That just shows the low calibre of installer and the poor quality of the installation!

Nor should there be no bypass. As a temporary measure I suggest you open it just a little until the temperature shows there is just a little flow.

I have no reason to doubt the boiler is fine apart from being connected to an unsuitable system.

To assess the situation i would be doing a thermal survey!

Tony

Tony

 

[kjharry]

Could it be that all the rads have thermostatic rad valves fitted where one rad should be permanently on ?,if they all shut down due to the temperature being achieved then the pump has nowhere to send excess heat from the boiler.

 

[Agile]

if they all shut down due to the temperature being achieved then the pump has nowhere to send excess heat from the boiler.

If the boiler had been properly fitted then it would have the auto bypass valve for the flow to continue through.

Tony

 

[Rover05]

No, atleast three wide open -- most throttled to half, they're all TRV's.
Gut says pump underperforming, but maybe boiler coked or airlocked.

 

[kjharry]

From the posts it looks like they are all trv's and no auto bypass.

 

[Rover05]

All the rads have TRV inlets.
What's an auto by-pass? I thought the mentioned bypass was a reference for the manual B/P near the pump - which I've shut to make sure 100% flow is driving thru' the boiler.
Not a plumber, a jack of all trades - boiler internals are beyond my expertise.
Edit: I believe the boiler is relatively new, ideal classic HE FF370

 

[Rover05]

BG will not be able to better the advice that Dave and I have given you!

Your problem is just that its 8 mm ( as long as thats clean and not blocked! ).

You should never have had a gate valve as a bypass! That just shows the low calibre of installer and the poor quality of the installation!

Nor should there be no bypass. As a temporary measure I suggest you open it just a little until the temperature shows there is just a little flow.

I have no reason to doubt the boiler is fine apart from being connected to an unsuitable system.

To assess the situation i would be doing a thermal survey!

Tony

Tony

Hi Tony, appreciate your efforts. The pipework/installation was done 15 years ago. Hence the 8mm bore - I believe the internals are reasonably clean. I did flush several times using mains pressure, than ran it for a while on distilled before finally draining and refilling with distilled and 5litres of Fernox. ALL rads get hot IF I open the TRV's fully.

At risk of repeating myself, reservations about circulation pump. Just checked the boiler and it's has cut out a degree below stat ask due to boiler cut out. I have been conservative with the boiler limiter. Local boiler limiter scale 1 to 6, running at 4 to 4.5. Frightened of burning out the boiler.

 

[Agile]

Flushing a system means a different thing to a boiler engineer! It means using appropriate chemicals and often using a power flushing pump! Not just washing it through with tap water.

It would help us if you could measure some temperatures starting with the flow and returns at the boiler.

Does the boiler cut out while the burner is on or afterwards?

Is the pump over run operating?

Tony

 

[Rover05]

OK Tony.

I'll be back..............in Arnie style with some temp measurements.
Incidentally when I ran it for a few weeks on distilled, it was dosed with de-scaler - drainings did eventually run clear. Like I siad pretty handy but boiler internals are not on my radar.

Cheers for all the contributions everyone.