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It's the noise rather than the longevity. I've spoken to a couple of different bods at Viessmann now and they tell me that on the 100W it can take as long as I mentioned for the pump overrun to stop. Due to boiler location I don't want to hear the pump rumbling on for an hour or more after I've...

Out of interest have you paid any attention to the pump overrun on these? Viessmann tell me it's temp controlled on the 100W and it can take over an hour for the pump overrun to stop, whereas on other boilers I've seen, it's based on time, usually 5 minutes. It was this unknown pump overrun time...

For the sake of completeness and if anyone reads this in the future I thought I'd post back my conversation with Viessmann technical. They say the pump overrun on the 100W is temp based, and after the demand for CH is turned off, boiler internal temp needs to drop by 34 degrees for the pump...

I know this gets asked a lot of times but still, everyone's needs are different so I would be grateful for any advice. I live in a smallish 3 bed detached house, just the one bathroom with electric shower, so HW is only required for kitchen sink, bath and basin, plus basin in downstairs loo...

Good points there stem. It's going from a traditional boiler to a combi but I'm wanting to keep hard wired controls, so a separate wall mounted thermostat and a hard wired timeswitch for the heating. I'm just not a fan of these RF programmable thermostats. There's currently the junction box...

Firstly, I’m not going to be undertaking any of this work myself, I’m just trying to get an idea of what can and can’t be done. At the moment I have the boiler spur, with the timeswitch/programmer right beside it and the boiler above it. The wiring is chased into the wall so it’s not easy to...

True, I may be over-estimating the time it would take for the temp to drop. I suppose it all depends on what parameter is set in the Viessmann for when the over run stops. Maybe 65 like you say, which shoudnt take too long to achieve from a peak of 80. I'd have thought for cheapness it would...

Fair enough Dan I do appreciate it's a bit of an open ended question but seeing as you're reading this, what's your experience with temperature based pump overruns? Do they tend to work like a thermostat and the system water has to fall to a set internal temp? Could it effecitvely take over...

Sorry to come back to this one but still trying to understand. For boilers that have a pump over run based on a temp drop rather than time, how long could the pump be running before it is satisfied and turns off? I'm talking about after the CH has been on, so the system water will be very hot...

Is it prone to blockages due to the 8mm orifice being smaller than most other TRVs?

Ok I think I get it now. So what happens when the CH is turned off with regards pump overrun? As the circulating water will already be very hot, won't it take ages to cool down? For temperature controlled pump overruns won't this take a long while to achieve?

The big living room rad will have no TRV fitted so will act as the bypass. The bathroom towel rail is also always open. Maybe it's the fan as well as the pump I'm thinking of when I hear combis 'running' when apparently Off. The fan just blows heat into the room where the boiler is?

Ok so a pump does run then! So where does the pump overrun circulate the water to? The CH circuit? Dan - you're often the fountain of all knowledge on here. With the pump overruns that run based on a temperatue drop rather than time, can they take a long long while to dissipate the heat?

Hang on, you're right and I was getting confused but something does continue to run after you close the HW tap. If it's not the pump then what is it? Or does the pump then kick in after you have closed the HW tap to disspiate the heat elsewhere? All I know is with combis, when you close the HW...

Got a Y plan at the minute but the pipework will of course be getting overhauled when I get a combi fitted. Not good to hear that the HW side of the combi boiler opens up to the CH side to dissipate the heat when the pipes are as noisy as mine.

My boiler and existing system's days are numbered, so I'm only focusing on the new system rather than repairing what I've got. Do you know the answer to the question i asked about where the heat disspates to on a combi after HW is no longer being called for? Is it recirclated round the CH...

Hit the nail on there Ian, noise nuisance. My current system (open vent, fully pumped) makes one heck of a racket due to inadequately secured pipework. When I get the boiler replaced, I'll be asking for all the suspect pipework to be reclipped as required but I still fear noise. That said...

Hi Pete, can you expand on this. Say I'm just finished calling for HW, does the heat then get dissipated to the CH circuit? If the heat is no longer heating up cold water, where does it dissipate to? As for why it bothers me, just a personal thing. Sometimes you only want a minute or so of...

Still looking for a combi boiler and having come into contact with a few over the years, I know that with some, after you've stopped calling for HW, the boilers pump continues to run for a couple of minutes, but with other boilers it's more like 10-15 minutes. I've been keen on getting the...

On most boilers I've seen, the PRV is routed through the outside wall and then back on itself, so if ever the boiler discharges any water via the PRV then you can see it. The Viessmann range seem to combine the PRV and the condensate pipe into one, so how are you supposed to see if the PRV is...