People on the newsgroup have mentioned the need for a bypass on the CH circuit. What exactly is a bypass and is it really necessary? I think this came up in a discussion about TRV's for rads because I wanted to fit more. I have a baxi solo boiler thats about 5 years old and I believe some boilers have an internal bypass.
(BTW we live in a reasonable sized house and the boiler stat is set on No.6, the highest. I think realistically we could do with a bigger boiler but presumably its ok to run the boiler for prolonged periods on setting No.6?)
I have a bypass on my Baxi AFAIK its to stop the boiler overheating when the zone valves shut and its just a tap between flow and return thats opened a small amount
Modern boilers hold a relatively small amount of water in comparison to the amount of metal in the heat exchanger. When a room stat interrupts a boiler and pump in full flight, the residual heat in the metal part continues to heat the water after the flame has stopped, with the result that overheating will occur unless water continues to flow through for a short time. For this reason, many boilers - including the Baxi Solo - control the pump directly, and keep it running for a bit after the boiler has stopped firing (known as pump over-run). In a system with zone valves and/or lots of TRVs, there may not be anywhere for the water to go during this over-run period. Hence the need for a by-pass circuit - which connects the flow and return pipes, and provides an alternative flow path. This is best achieved by using an automatic by-pass valve which only opens when the pump pressure is higher than normal due to everything else being closed off. Some boilers have built-in by-passes, inside the casing. As far as I know, the Solo doesn't.
The Solo doesn't mind running on its max setting for long periods. The acid test is whether it manages to keep up with the heating demand when the weather is very cold. You may well find that it has several heating capacity settings which can be selected by adjusting the gas pressure. Information about this is in the inatallation manual, and probably inside the boiler casing. If it isn't on its highest setting, you may be able to get a bit more out of it.
Thanks for the info. We have recently moved in and unfortunatley the previous owners didnt leave us any boiler manuals. I will try to contact Baxi and see if I can get a copy although its probably no longer made.
I will add the extra TRV's to the landing and lounge rads. Have been told that often the bypass is a rad that is needed to be hot whenever the CH is on such as a bathroom rad. For our system this wont have a TRV on it.
You'll probably be able to download a manual from Baxi-Potterton's website.
The best solution may depend to some extent on your system layout. You are likely to have either one 3-port motorised valve (Y-Plan) or two 2-port valves (S-Plan). Which have you got? If you're not sure, you may get some pointers from
You can get the manual for the Solo 3 from their wibble but for the 2 you'll have to phone up and they'll send you a (photo) copy.
plan and you don't need a bypass as long as one rad is permanently on (with non-adjustable valves at each end). This could be the bathroom rad or current practice is for it to be the rad in the room where the room thermostat lives. This room should not have any other source of heating such as a gas fire.
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