Any Plumbing/Heating peeps here
 

Right

im just having a Valliant 418 Heating boiler put in (open vented, S-plan). Its a straight swap from the old one to new one, some piping needs to be done, electrics are all ok. Now the issue is that the boiler needs the pump wired in to overrun when the timer (external) shuts the system down, when this happens the valves close but the boiler keeps the pump running, the installer wants to put a by-pass in, but without a auto by-pass valve, just from after the pump to the return flow.

I thought it needed a bypass valve so that the water only bypasses when the valves shut and the pump is in overrun, otherwise you will circulate hot water straight back to the return while its running. Granted he is installing the by-pass in with a smaller than 15mm, which would mean that the flow is mainly going to the heating.

I think hees a little confused as he mainly puts in system boilers and combi boilers and we are having a convential condensing heat only boiler.

Re: Any Plumbing/Heating peeps here
 

I deal more with the commercial side of things rather than domestic, but I'm not quite sure what you mean by 'system' shuts down. The pump needs to run on after the boiler shuts down to prevent the boiler over heating, no bypass required.

The only time you'd need a bypass is if you've got thermostatic radiator valves, so that if they all shut you've got some form of pressure relief. In that case a bypass, whether it's fitted with a valve or not, should do the trick.

Re: Any Plumbing/Heating peeps here
 

I thought you always had to have at least one radiator (usually bathroom) in the system that didn't have a thermostatic valve on it, that's what i was told just before i installed mine.

Re: Any Plumbing/Heating peeps here
 

tis correct.

Re: Any Plumbing/Heating peeps here
 

That's the alternative to having a bypass. A bypass will however save energy, being as you're not throwing heat out of a radiator just to allow water around the system.

Re: Any Plumbing/Heating peeps here
 

Well if you have the flow comming from the boiler, to the pump which then splits into 2 valves, one CH one HW, if they are both closed because the timer has turned off, the boiler keeps the pump running, it will be pumping nothing, so the by-pass is takes off between the pump output and the valves and goes to the return flow into the boiler, but when the system is running, you dont want any bypass to happen as the valves are open. So having an auto by-pass valve in the by-pass loop, it will open when the pressure diffirential changes between the flow & return loops.

Not sure if that makes sense.

Re: Any Plumbing/Heating peeps here
 

we only have the bedrooms with TRVs, the rest of the rooms dont have them as they never get that hot

Re: Any Plumbing/Heating peeps here
 

Okay you'll need a bypass pressure relief controler as if you don't then the pump wil be pumping against a closed head and will eventually knacker the pump. The pump will run on to disapate the heat, as an alternative can the guy not link out the run on timer so that the pump will cwitch off when the timer goes off. The valves (2-ports I assume) will not just close striaght away they'll probably take 10 -15 secs or so.

Re: Any Plumbing/Heating peeps here
 

hBefore i had wired the system so the timer controled the pump, but now as its a new Vaillent 418 condensing boiler, the pump has been removed from crontrol of the timer to control of the boiler (wired direct to the boiler circuit board), the boiler has a perm live so it can control the pump, ive gone into diag mode and it does not allow the pump overrun to be turned off, only decreased to 2mins. The valves flip the micro switch within 2s of the power being cut to the servo.

The way he has put the bypass loop in, when its open ive noticed that it keeps the boiler temp too high and it throttles the output to maintain a 75c water temp and the rad temp starts to go down. At the moment, as the timer is perm on ive shut the by-pass so it heats the house faster as its had no heating for the last 5 days. The loop has a ball stop valve on it, so i was thinking of removing it myself and putting in a by-pass valve, problem is i mayl have to drain the system, unless i just shut the valve and then cut more pipe and put it between the pump and ball valve. Other problem, is he has put the by-pass pipe as 15mm but i can only find 22mm by-pass valves.

Hees in tommorow, so i may just be insistant and get him to put it in when he drains the system again.

Im not an installer, but i know how to read manuals and have a good understanding of how it all works.

Re: Any Plumbing/Heating peeps here
 

He's installing the bypass the old fasion way. We remove alot of gate valves and ball valves now and replace them with a auto bypass that works on pressure, they should be 22mm really so the flow rate will remain the same with the valve open thus lowering the temp on pump over run quicker..

It needs this to prevent the pump from pumping hot water nowhere.. Like has been said in theory all of your rads could have TRV's on and they could all shut down, if this happens then theres nowhere for the water to go. The bypass should be set to prevent it opening on normal operating temperatures, it should only open if the pressure increases i.e because the valves have shut.

Good boiler the Vaillant thats all we fit and have only had a hand full of problems on the thousands we fit.. 2 years warrenty too i think with yours, their customer service is very good!!!

Oh and make sure he balances the system too, i.e turning down the rads that get hottest first to throw some of that heat to the other buggers rads perhaps!!!

Hope im helping in some way!! :D

~Rich~