Vaillant F70-4 Boiler Replacement Advice

Old 05-26-14, 09:26 AM
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Vaillant F70-4 Boiler Replacement Advice


I need to replace my leaking Vaillant F70-4 boiler. I have a Riello F5 burner with a .65 gph nozzle ( .75 gph @140 psi). The system has 4 zone valves: 1 indirect DHW tank zone , 3 heating zones for baseboard radiation. Heat loss is calculated to be 54,000 BTUs at 70 deg/0 deg design temperatures ( Suffolk County/ NY). The heating zone losses are 21,000, 17,000, and 16,000. I don't know the water content of the Vaillant. Is it considered a low mass boiler?. I am looking either a Biasi B10-B-4 or a Buderus G115ws/3. I want to keep the system design very simple and since I only use about 600-700 gallons of oil( lower thermostat settings and setback thermostats and zoned living spaces closed off), I am not expecting any huge reduction in oil consumptions to pay back cost of expensive complex system ( primary/secondary loop, buffering tank etc). I would consider a smart aquastat and an Outdoor Reset Control. Any advice would be appreciated. Thanks
Old 05-26-14, 03:33 PM
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I gather that the "leak" has been determined to be totally irreparable?

This seems like an enormous project to replace a boiler, which in my mind, sounds like it's still a youngster itself.
Old 05-26-14, 04:22 PM
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Don't dismiss the Burnham MPO, that should be on your list also.

MPO-IQ115 - Burnham MPO-IQ115 - MPO-IQ Series 85,000 BTU Output Oil Fired High Efficiency 3-Pass Boiler

I replaced my Vaillant F70 with that one and the fuel savings have been, if not dramatic, quite notable. 2000 sq ft home, 475 gallons this past winter, and 450 the winter before. This is with a constant 70F setting on t'stat. I'd have to refresh my memory by pulling out my records, but I believe that the last winter I used the Vaillant was at least 100-150 gallons more.

I hated that boiler. What a piece of shyte design...

ANY excuse to replace a Vaillant, in my opinion, is a good one.
Old 05-27-14, 04:55 AM
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And don't forget the MPO-IQ has an OD reset plug in card soon to be used with a wireless sensor. The card has many features which includes priority protection.
Even though I am not a big fan of domestic hot water priority this feature is used by many contractors. What this feature does is if the DHW does not satisfy within a designated time, the heat circulators will come back on anyway.
For more info goto and see the ODR control manual.

Last edited by NJT; 05-27-14 at 05:51 AM.

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