Flexicom Boiler slow to heat up, anything wrong?

[macsco]

Hello
New boiler fitted Flexicom SX30 system boiler only heating radiators, (replaces a Baxi 105E combi).
Everything works no fault codes, no lock out.
The water temperature is set to 80C and max power is set to 30KW, from a cold start the temperature gauge rises slowly and after about 4/5 minutes the tpi room thermostat turns off (in anticipation) yet the 30kw boiler has only managed to get the water up to about 50C and the return is not much more than warm.
Eventually all rooms get to temp after a few cycles but it is a lot slower than the Baxi.
The Flexicom is a fully modulating boiler, it will go down to about 10KW, and I suspect it is doing this despite the settings.
Perceived problem is only on start-up.
So is there anything wrong? or is this just the way it is? I would expect full tilt at 30KW and THEN modulate down.
Thanks

 

[terryplumb]

If all your rads get hot to touch within 15 mins of c/heating being turned on you shouldnt worry about the boiler. You stated the boiler only heats radiators ?? What about domestic hot water ,surely it does both ??

 

[macsco]

Hello terryplumb
Yes all rads get hot, it is just the slow start, or should I say slower start than the inefficient Baxi
And yes it only heats the rads. Water is totally separate.

 

[terryplumb]

Just curious ,what heats your domestic hot water ?

 

[macsco]

Greenspring CWi47 water heater
And to pre-empt your next question, No it is not starving it of gas.
Meter upgrade, and turned it off in case it was the culprit. No difference.

If I could ask,
my interpretation of modulation is full tilt and then reduce to conditions, ie. flow and temperature.
If it's not going full tilt at startup what could it be?
Or am I getting modulation wrong?
As I write this I think gas blockage?
Pretty sure the boiler has a run at full tilt mode to test something, I think I will see if I 'force' full tilt and if it's no different, then relax.

 

[wannocks]

How many radiators do you have? 30Kw could be far too powerful. If this is the case it will cause the differential (difference between flow & return temperature) to be too high. The boiler will back off to minimum output if it goes over 30C.
Also intrigued. Where did you get a new Flexicom from? They stopped making them in 2015.

 

[macsco]

14 rads total, but a bit of zoning going on.
Have I had it that long,
The boiler came out of its box last month, but I have had it a while waiting for a long stalled extension to be finished..
The boiler can be range rated, worth reigning it in for a trial?

 

[nwgs]

What sort of thermostat do you have ? Is it the same as when you had the Baxi

 

[macsco]

Same not changed, honeywell cm707.
What you thinking - it's still on old learning?

 

[wannocks]

Try downrating it to 20Kw

 

[muggles]

30kW running 14 rads? That sounds way oversized to me, and a 3:1 modulation ratio (only able to drop to 10kW) is crap, especially if you've got some zoning on that as well. I suspect the boiler can't get its heat away fast enough and so is dropping to minimum output.

If you're aiming for an 80°C flow temperature, the new boiler won't be any more efficient than your old Baxi. Condensing boilers only condense when the return temperature is below 53°C, and systems should be designed with a 20°C differential between flow & return. If you're at 80°C flow, that's 60°C return, which means it won't condense. If the differential is too wide, the boiler will go into minimum output to prevent overstressing the heat exchanger. If that doesn't work, it'll cycle on and off, which is a terribly inefficient way to run it, and it'll also massively increase wear & tear.

In short, you've got the wrong boiler for your system (and it doesn't comply with modern Building Regulations either, so it can't be truthfully signed off as a compliant installation).

 

[picasso]

The heat exchangers on these boilers are very restrictive, you probably need a bigger pump or ccts.