Valiant Ecotec 428

When we moved into this property we had an oil fired boiler with a Grunfos pump. It was incredibly inefficient and was getting through £300 of oil a month. We changed it out for the Valiant 428 and our heating bills certainly took a tumble.
But I was still not impressed with the time it took to heat the house up. I used to joke that at time it was about 1 degree and hour. But I've seen worse than that when it's cold.
The Grundfos eventually died and Homeserve sent a man round and he changed the pump for a Circulating Pumps CP50.
Now it was only some time after that I started to really look at the issue and the recent cold snap has highlighted that something is really not right.
The CP50 is the smallest of there range with the CP60 being their better flowing/head pump.

Now this is an older detached house with 19 radiators. My gut feel is that the pump is really nowhere near adequate and that they have fitted the wrong device. But I can't explain why the previous Grundfos appeared to have similar performance. But I'm not familiar with their range and maybe it was similar to the current one in terms of performance.

During my investigations, I have spent some time observing the system in operation. When the boiler comes on, it takes about 20 - 30 seconds to heat the water up to the selected temperature and then it turns off. Because, I think , of the anti cycling timer. It then doesn't come back on for 20 minutes (Standard Valiant setting).
So in that time, the water has mostly cooled off.
So this doesn't feel right. In each hour it gets roughly 1 minute of boiler heating the water. No wonder it can take many hours for the house to warm up.

I changed the anti cycling time from 20 to 10 minutes but the weather has turned warmer so it's difficult to compare now.

So I'm trying to work out what's going on. I think what I'm observing is such a slow flow rate through the boiler that rather than heat all of the circulating water in the system. It's basically heating the water inside the boiler then turning off. Improving the water flow will mean that it'll have to heat more water and therefore the 20 seconds of on time will increase dramatically so that it heats more of the circulating water.
I've just purchased a Grunfos UPS3 15-50/65 which looks like a good upgrade and am about to try it. But of course it may still not be up to the job.

The resistance of the heat exchanger and pipework to 19 rads will kill a 15/60, I would be looking at a 25/80 or as you have bought a 15/60 another 15/60 in series would work just as well,

I have oil fired boiler, 15 radiators, 3 floors, and annual bill around £300, the boiler is rather simple, plumbing is C Plan so seems something very wrong with yours.

Each radiator except bathroom has two controls, a TRV and a lock shield valve, mine are not set correctly I know, mainly as wife has put things in the room so I can't reach the lock shield valve, but in real terms even with all TRV heads set to max the rooms should if the lock shield set correctly be around the same temperature, the TRV is only fine turning.

Some boilers monitor temperature of feed and return, and some only the feed, but the boiler can only get the water to a set temperature and if the plumbing means it all goes through one radiator then only that radiator will heat up. I have tried to balance mine with a point and record thermometer and will admit not very good, but still better than nothing, should be 20°C between feed and return on each radiator and until that is set, no point looking else where.

19 rads in parallel (assuming a normal two pipe system) will have a lower resistance to flow than 4 or 5 rads, so the number of rads in this case is immaterial. In hot water only mode there is little external resistance to flow, therefore the flow through the boiler should be high. The hydraulic resistance across your boiler is important, and it suggests that the boiler's heat exchanger has a partial blockage. From my experience the type of multicoil HEX in Vaillant boilers (that's VAY-LANT - correct spelling clearly marked on the front of the boiler) is prone to blockages, and may need specialist action to remedy it.
How old is the boiler? Did you have the heating system properly cleaned when the boiler was fitted?
Repair the boiler and your heating problems will go away.

MeldrewsMate said:

19 rads in parallel (assuming a normal two pipe system) will have a lower resistance to flow than 4 or 5 rads, so the number of rads in this case is immaterial.

Click to expand...

That's interesting, could you expand on that pet theory ?

No problem.
Take one straw, put it in your mouth and blow air through it.
Take two more straws and similarly blow through three straws in parallel. Is it easier or harder to blow?
Shall I wait while you find the straws?...

No I think I can manage without the straws, so going with your theory the more rads I have the smaller the pump, grundfos could bring out a 15/1 and you could have 50 rads on it, I think you have spotted a gap in the market here meldrewsmate.

The whole system was power flushed on installation continuously for a couple of days whilst they re-sited the boiler. The performance was the same for the Valiant from day one and it didn't seem to offer improvement from the old oil boiler. So I doubt it's a blockage in the boiler.

Interesting thread

https://www.diynot.com/diy/threads/flow-rate-in-central-heating-system.206079/

Same boiler as you, similar issue by sounds of it.

Turned out to be his pump was sized incorrectly

sxturbo said:

Interesting thread

https://www.diynot.com/diy/threads/flow-rate-in-central-heating-system.206079/

Same boiler as you, similar issue by sounds of it.

Turned out to be his pump was sized incorrectly

Click to expand...

Thanks for replying. That thread talks about a Glowworm Ultracom 38hxi boiler and a pump starting much bigger. Did you post the right thread?

I do accept that the new pump I've bought may still not be large enough. But it will bolt straight onto the existing fittings. The other pumps will need a change in the size/spacing of the connections and I'll probably have to employ a plumber to fit. So costs jump to £400++

thanks again.

MeldrewsMate said:

19 rads in parallel (assuming a normal two pipe system) will have a lower resistance to flow than 4 or 5 rads, so the number of rads in this case is immaterial.

Click to expand...

You're right the number of rads is immaterial, but it usually indicates a large system, which equates to longer pipe runs. The only thing which is important is the highest resistance - aka the index circuit. This combined with the resistance of the boilers hex (which is very high on these boilers) will dictate the pump head required.

steve compton said:

Thanks for replying. That thread talks about a Glowworm Ultracom 38hxi boiler and a pump starting much bigger. Did you post the right thread?

I do accept that the new pump I've bought may still not be large enough. But it will bolt straight onto the existing fittings. The other pumps will need a change in the size/spacing of the connections and I'll probably have to employ a plumber to fit. So costs jump to £400++

thanks again.

Click to expand...

The glow worm is the same as a vaillant 400 series as you have which is why it's relevant.

The pump required in that thread is bigger because his system and heating requirements were much larger. However his issue is very similar to yours and was caused by an undersized pump.

Your new pump is likely still undersized as has been suggested by Picasso. But need to do some calculations and such like. Or as has been suggested install a 2nd identical pump.

We dont really know what the OPs actual symptoms are, as there's been no information given about what the boiler flow/return temps are when firing and what S codes are displayed. Is it inadequate flow? Is there an ABV? How is it set?

I know these diagrams are for a larger kW boiler than the OP but compare the modern 38 kW formed tube Vaillant heat exchanger (top diagram)
with the lower ancient cast iron Potterton heat exchanger

At 1600 litres/hour (6 gallons/min) look at the head loss figures on the Y axis.
The Vaillant heat exchanger has a pressure drop of 400cm (water gauge) whilst the old 50kg lump of cast iron runs at just 5 cm.

#


After circulating the water through the modern heat exchanger there is little residual head left when using a standard 5 or 6m pump.

Just to update.
Theory proved correct

I replaced the CP50 pump for a Grunfos UPS3 15-50/65 as it looked like the best performing pump that would fit onto the same fittings.

The difference was chalk and cheese.

The house is a big old house and now the temperature, as displayed on the boiler, rises much more slowly as it is now heating the water passing through the boiler until the whole system is hot. I've currently set the boiler to a high 75 Deg. in order to get as much heat into the house as soon as possible.

All 19 rads now get scorching hot, top to bottom, in 30 minutes. But importantly the boiler isn't cycling on/off constantly.
The house takes some time to warm up. But I don't think that I can particularly lay this at the door of the current heating system. I may need to upgrade a handful of the radiators for doubles and look at insulation in the property.

The graph on the 438 pressure loss is interesting and in some ways I'm a little surprised that the Grunfos pump at 6.5M made such a huge difference. But it did. Like night and day.

At some point, I'll measure temperatures of flow/return. I suspect the new pump is just adequate. But for now, it's just great to have a house that I can heat.
Thanks all.