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

[MikeAustin]

Hi Chris,
You seem to have a similarly lopsided system to mine, due to having the boiler repositioned. Mine is in the garage - uninsulated, draughty and with an up-and-over metal door - not much different to being outside. I found that the system is critical to radiator balance and keeping the return temperature high - and I attracted some mockery here for lagging the return pipes at the boiler! My lockshields are open between 3/4 turn and 4 turns (full). I feel this may indicate an inefficient setup. What is your lockshield range?
My old boiler kept dropping its pilot light. After several months, I got someone in to look at it. He suspected a leak round the casing, although he could not actually find it. He condemned the boiler and put a "do not use" tape on it. I persevered with the pilot and it was OK for a year or so. After that, I decided to go for a bells and whistles new boiler. Initially, they could not get it working at all. Then they found that the old boiler had been running backwards, so flow and return had to be swapped. Ah those were the days when boilers were so versatile - days when one could adjust carburettors and clean contact breakers, days when I could rewire my house, days when I could take people for countryside walks without doing a risk assessment ... but I digress!

 

[Agile]

With a condensing boiler the rad differential should be closer to 15-20 C. That allows the boiler to condense and gives greater efficiency.

Why did you want 11 C ? That's the old figure for a non condensing boiler!

TRVs are bi-directional and it makes little difference which way round they are fitted.

Weather Compensation is very good if left to itself and not fiddled with all the time.

But when used the boiler has to be connected so that when its heating the cylinder it gives a higher output temperature of about 70 C.

That means a hot water priority system that only heats the cylinder when that is required.

Some boilers have this provision built into them with a four pipe output.

Have you closed your manual bypass yet? What effect did that have?

Tony

 

[FlyingBrick]

Thanks Tony for the information. Appreciated.

Went into the FAQs section for balancing rads and that gave a 12 C differential that I used.
As in my previous email I have not closed the manual bypass yet as there is a weep at the spindle end and the slightest movement to turn it around starts hot water creeping out. Now have a new valve to swop it out later this week when the miss's lets me partially drain the system down and turn it off.

The Viessmann used is connected just with two pipes with one Honeywell valve for the HW and one Honeywell valve for the CH. These are turned on in any order by the Potterton EP2 timer.
Again thanks for the TRVs as I had found just one connected round the other way with the thermostat on the outlet while the other 13 connected to the input.

Chris

 

[Agile]

So your controls would need modification to give hot water priority if you want to use weather compensation.

Tony

 

[FlyingBrick]

Thanks Agile info the info on hot water priority.

Have now realised why the plumber did not take out the faulty bypass valve. It was positioned directly behind the insulated copper tank in the airing cupboard with a gap of only 7inches to the wall. Also the bypass 15mm pipe was sitting in between two 22 mm vertical pipes so could not use my hacksaws or a pipe cutter to make a larger gap for the new valve. The only way I could see to cut out a section was using a Bosch GOP250 vibrating tool with a small long cutting blade to gain access behind the tank.

Worked a treat and new valve in place with two bottles of MC1 inhibitor. Slowly getting there at last. The old valve was pretty well seized up and now when the bypass is turned on very little noise and no cavitation takes place. Can sleep at night Sorted.

Many thanks to all who helped out with my problem. It was appreciated.