New Viessmann 100-W taking longer to heat up than old Ideal Classic NF70 unit

[D_Hailsham]

Well actually, I think you should.

You're the one that said Muggles was wrong. Perhaps you should explain more fully why.

I was questioning Muggles assertion that heating up a house slowly (to reach a set temperature) is more gas efficient and comparing it to accelerating a car slowly or quickly to achieve a set speed. It was only the comparison why I found flawed.

I agree that running a boiler at lower temperatures will improve its efficiency due to increased condensation. But it will still need to provide the same amount of heat whether the house is heated in 30 minutes or 3 hours. Whichever method is used, the heat input has to be greater than the heat loss or the temperature will not rise. There is, of course, a limit as to how slowly you heat a house.

If what Muggles (and, presumably, you) say is true, Honeywell etc should be designing their controllers so they heat the house up slowly; but they don't. They engineer them so max output is provided initially and the boiler is only backed off when the house is within a degree or so of the required temperature. I'm not sure what happens when weather comp and Opentherm controllers are used.

 

[Dan Robinson]

Showing some big knowledge gaps again their I'm afraid.

 

[Steelmasons]

I enjoy reading DH posts.....especially the post whereby he suggested air for combustion was taken downstream of burner , the boiler in question being the one hanging on his wall.....

 

[D_Hailsham]

Showing some big knowledge gaps again their I'm afraid.

So, educate me. I'm not too old to learn; and I won't be doing you out of a job.

 

[Dan Robinson]

Heating the house slowly means running the boiler slowly.

More efficient. They have fans that shift air. Hot air.

Honeywell etc should be designing their controllers so they heat the house up slowly; but they don't. They engineer them so max output is provided initially and the boiler is only backed off when the house is within a degree or so of the required temperature. I'm not sure what happens when weather comp and Opentherm controllers are used.

A total lack of understanding of how boilers and controls work displayed there. I'm even sure where to start frankly.

 

[Phill Peck]

Haven't read all the posts but....
For starters get your installer back to finish commissioning
And you say small bore the Viessmann heat exchanger is one of if not the largest bore of a domestic heat exchanger.
@Agile im afraid in this situation your advice is wrong. An auto bypass will make this situation worse.

The way the Viessmann OV works, it will fire at a low rate and modulate up as the return warms. What is needed on larger OV's is a bypass almost acting as a mixing valve to provide a small amount of heat back into the return keeping the temp up to keep boiler firing.

I try to avoid installing larger output OVs

Fire the boiler and watch the flame bars it should fire around 2or3 bars and will then sit on 1 or 2 until flow is established by the warming return.
Not sure why they have done this as the boiler has a flow switch so flow is easily proven.

 

[FlyingBrick]

Hi gasservice1985

I was comparing the big heavy cast iron heating boiler to a modern spiral heating tube where the transfer of heat would be faster than trying to heat up a big lump of cast iron with the burner at the bottom going full blast as my Ideal NF70.

The Veissmann goes up to 3 bars fairly quickly then drops down to one on my open vent system. Not being a plumber and have not installed a full system I was only working on some old schoolboy physics. I was looking at the bypass valve that stays open at something like a third of full flow so letting hot water go straight back to the return of the boiler therefore giving it the wrong signal that the 14 rads were warmed up and therefore the burner could be dropped down. The system worked ok on my old boiler because there is no return temp probe to compare the inlet and outlet pipes just a thermocouple pushed into the cast iron boiler and running at full all the time.

So my thought process was by taking out the fixed bypass valve on a 15mm loop just before the two Honeywell valves and sticking in a Danfoss AVDO15 valve would stop the hot water returning straight back to the return of the Viessmann until the rads warmed up quicker and then the valve would start to open allowing some of the hot water to return via that route plus of course the rads.

Also as the old bypass cheap naff valve causes a lot of cavitation once the rads were up to the set temp the water flows down the loop at greater volumes making a lot of noise late at night in the airing cupboard next to my bedroom. With CH and hot water on there is around a 13* temp drop between the two by the boiler downstairs. With just HW only there is a drop of around 9* between input and output. Outside temp around 3*centigrade.

As it took my gas safe/plumber three months to turn up and replace the NF70 boiler I did not want to have to wait until spring for him to sort it out having waited so long

Does this make any sense or am I totally lost in copper piping?


Chris

 

[Dan Robinson]

Your boiler doesn't have a return sensor.

 

[Phill Peck]

Your boiler doesn't have a return sensor.

The latest OV does Dan don't think the earlier ones did.

OP as I have pointed out an auto bypass won't help.

When the boiler modulates down to 1 bar....
What temp is displayed on the screen?
How hot do the 2 pipes feel? More importantly the return (right hand pipe)
Do the radiators all get hot eventually?
Edit extra question
What setting do u have the dial on?

 

[Phill Peck]

Just re read original post.
Your bypass valve is an isolation valve?
Completely the wrong valve, can't believe someone would install that/leave it in. That will be the cause of the noise u mention. It also offers very little in terms of balancing. Get that out and replaced with a gatevalve (preferably a manual bypass valve but gate valve will do)

 

[Mike_Sammon]

Just get the installer back or say where you are based and you could pay someone local here to sort it all for you.

 

[FlyingBrick]

Spot on gasservice1985 many thanks for taking the trouble to reply.

It is the standard cheap isolation valve with the silly blue plastic lever that always breaks off as used in washing machine fittings before the plastic water pipe. The plumber installed this when the house was first built also I noticed the arrow on the body is facing the wrong direction to the actual water flow from the pump. Not surprising that the racket emitting from that valve is like a quite food mixer running when the rads are up to temp and a larger flow try's to go through the 15mm by pass loop with that valve in the middle. He also installed a water softener round the wrong way and we had a cold water tank in the loft and a shower full off resin beads. Told me he had not made a mistake so I put them round the correct way as shown in the Permutit installation manual. No problem since.

When the boiler modulates down to one bar it is reading 70*C output with the dial setting on full position 6. Return pipe just above boiler reading 63*C using my Fluke infra red pyrometer. Outside temp around 5* yesterday. Had measured the temp between the two pipes directly above the boiler top say 20cm (black tape on the pipes) and get with CH and HW on a difference of 13-14*C.
With just CH only on I get around a 9-10*C temp difference. Outside temp again around 5*C.
I find it annoying about the valve having actually shown the chappy the set up and pointed out the isolation valve that had shown a very slight weep on the spindle and he made no comment let alone throwing it out of the window. Just in a rush to get to another job before Christmas Eve.
My faith in builders and plumbers has recently been dropping as some of the things I have come across I just could not do and walk out of a persons property with some of the bodges.

I am around 5 miles East of Norwich near a place called Poringland by the way.
Pity I don't still live in Royston as I would be phoning yourself to check out the work done just before Christmas.

Chris

 

[FlyingBrick]

Back again gasservice1985

A MagnaClean professional 2 filter had been added to the return pipe just above the boiler with the new Veissmann.
Today with just the CH only on and not going through the copper tank with dial setting of 6 I get a reading with one bar showing of 65*C output and 55*C return to the boiler.
Did take the magnetic filter out and just a very small accumulation of iron oxide that was wiped away quickly since Christmas Eve.

Chris

 

[Phill Peck]

atvtgis point with the temperature stated are the rads hot?

In this situation it sounds as though you are getting too much flow through the bypass.
The valve you have needs to be changed as per previous post and system needs to be balanced imo.
Can't say more with out being there really.
Check the sticky at the top of the forum with regards to balancing.

 

[FlyingBrick]

Thanks gasservice1985

Will take the isolation valve out next week when I can drain the system to copper tank level.
Take it you prefer a manual valve and not a automatic Danfoss AVDO15mm Bypass valve to replace it?
Could you tell me the advantage of not using an automatic expensive valve (aprox £50.00) and which make and type of manual bypass valve to go for 15mm pipe work.
Many thanks again for your patience. Will also try and contact Mr Gas Safe to see if he will return. Not going to hope for to much. Also I presume he has to contact the right authorities for the paperwork to go through?

Chris