Vaillant 418 s53 & s7 after New radiator

[rbranco]

I'm having the dreaded s53 problem and also s7.

418 ecotec plus (10yrs old)
15-50 pump
External controls (pump boiler controlled)
2 zones (CH and HW)
ABV After pump but before valves, back to return circuit
Magnaflow

10 radiators (one is 2m long single, one is 1.9m high double 8kbtu, rest are mix of double and single 1.5m approx).
From boiler to top boiler (top of radiator) in the system is about 6m.

Recently installed new radiator in one of the upstairs bedrooms from a long 2.5mx40cm single panel to a 40cmx1.9mh double panel vertical radiator. At the same time we installed a magnaflow and replaced the ABV due to it being broken.

Since it the boiler will now cycle s53 with the deltaT being too large or if the HW loop is open it can s7 and shut down as the flow temp shoots up to 75 very quickly.

Could the new radiator which has increased the highest point in the system now have caused an issue with the pump sizing?

Also the when the system was fitted the installer fitted the ABV going from flow 22mm->ABV->15mm->22mm return, I suspect this can cause an issue as it never seems to bleed the hot water into the return unless the valves are shut but the pipe still gets hot.

Today has been a nightmare as also one of the valves started bussing the tripped the fuse, it had enough só was replaced and also found the other valve microswitch had arc'd closed keeping boiler running 247 so I fixed that switch. It's one problem after another at the moment for me.

 

[John D v2.0]

Could the new radiator which has increased the highest point in the system now have caused an issue with the pump sizing?

No, the highest point only affects the charge pressure needed in the expansion vessel and the cold fill pressure.
The extra volume in the system would need a big enough expansion vessel, but you'd see water coming out the pressure relief not temperature issues.
Your first issue is probably too much heat loss in the system or the pump is not getting the water back to the boiler quick enough. Either that or a restriction in the system. The boiler won't keep heating for ever if it doesn't see the heat coming back. Balancing the system differently might help, do all the rads start to heat up together?
With the cylinder it's only a small circuit with not too much heat loss, so the boiler would shut down until the primary temperature drops. Maybe your hw coil only drops a few KW, so once the water is almost up to temperature it's below the minimum output of t boiler. That's normal if the boiler and he target temperatures are similar.

 

[picasso]

What speed is the pump on? 418 is normally on open vented systems is your sealed or open ?

 

[rbranco]

Sorry forgot to say it's an open vented s-plan system.

 

[rbranco]

What speed is the pump on? 418 is normally on open vented systems is your sealed or open ?

Open vented, Speed 3

 

[rbranco]

No, the highest point only affects the charge pressure needed in the expansion vessel and the cold fill pressure.
The extra volume in the system would need a big enough expansion vessel, but you'd see water coming out the pressure relief not temperature issues.
Your first issue is probably too much heat loss in the system or the pump is not getting the water back to the boiler quick enough. Either that or a restriction in the system. The boiler won't keep heating for ever if it doesn't see the heat coming back. Balancing the system differently might help, do all the rads start to heat up together?
With the cylinder it's only a small circuit with not too much heat loss, so the boiler would shut down until the primary temperature drops. Maybe your hw coil only drops a few KW, so once the water is almost up to temperature it's below the minimum output of t boiler. That's normal if the boiler and he target temperatures are similar.

Open vented
I was thinking about too much heat loss but then changed my mind as it goes into s53 within 1m of starting which would never be enough time to circulate water around the system

 

[Gasguru]

It appears that the flowrate through the boiler is too low.

What setting has the new bypass been set to?

You need a minimum flowrate through the boiler...what was the old bypass set for?

Try setting it to 2m as a starting point and see if things improve.

 

[rbranco]

It appears that the flowrate through the boiler is too low.

What setting has the new bypass been set to?

You need a minimum flowrate through the boiler...what was the old bypass set for?

Try setting it to 2m as a starting point and see if things improve.

I've tried everything from 1 to 6 makes no difference. I have a feeling that the way the installer reduced the pipe from 22 to 15mm then back to the 22mm return may cause it not to function correctly.

Minimum flow, the pump should take care of that, the bypass really should only trip in when the valves shut or TRVs close but any I have in the house are set to max anyway.

 

[John D v2.0]

If the reads are all open the bypass should be closed, sounds like the pump isn't pumping enough water. Are the rads getting warm together before it cuts out?
Edit at 40 litres a minute the water woulds have got half way round the system by that time, the boiler flow should still be fairly cool but the rads should be warming a little at the inlet end

 

[rbranco]

If the reads are all open the bypass should be closed, sounds like the pump isn't pumping enough water. Are the rads getting warm together before it cuts out?
Edit at 40 litres a minute the water woulds have got half way round the system by that time, the boiler flow should still be fairly cool but the rads should be warming a little at the inlet end

Some get warm others stay cold until the system temp rises which can take a long time.
When it throttles back only a couple of the rads nearby are getting warm.

 

[dilalio]

Air or crud in the boiler/system from the drain down and refill. Can you bleed the boiler? Have you bled the pump?
Try those then check pump is spinning freely then drain down again and try and flush things through. Did the F&E cistern have a load of Shyte in it when you drained?

 

[rbranco]

Air or crud in the boiler/system from the drain down and refill. Can you bleed the boiler? Have you bled the pump?
Try those then check pump is spinning freely then drain down again and try and flush things through. Did the F&E cistern have a load of Shyte in it when you drained?

Other than a air bleeder on the return flow I can't see any other.
The system was drained then the magnaflow + rad installed, within 30mins of system being filled it had caught a load and since even more, I would say about 1/3 full in just around 2 weeks, considering system had nothing in 10 years not all that bad.
I opened the pump bleed screw and it started to dribble out, no air, did not check if it was spinning free but ile do that.
The f&e tank always had a surface of slime etc but not proper crud I could see, now I've put a lid on it.

 

[John D v2.0]

I would say about 1/3 full in just around 2 weeks, considering system had nothing in 10 years not all that bad.

that's just the circulating crud, a lot of it will just sit there not really moving just slowingng things down. Might help to flush through under mains pressure turning off all rad except one in turn.

 

[Gasguru]

Look in the manual..these boilers are hyper sensitive to flowrates and you will need the bypass to achieve a minimum flowrate when most of the radiators have shutdown.
But it does sound like there are other problems with circulation.

 

[dilalio]

As above. Mains flush it and get the crap out - then you know what you’re dealing with for the abv and flow rates.