CH pump advice please

[Tim+]

Our CH pump is getting increasingly noisy and there?s now a pretty constant irregular ?grumbling? rumble whenever it?s running.

The noise is aggravated by it being horizontally mounted in the loft (where the boiler is) and it seems to use the ceiling as a sounding board.

Anyhow, it seems like this would be a good opportunity to replace and relocate the pump to the airing cupboard where I should be able to mount it vertically away from any resonating surfaces. I?m assuming that it?s reasonable to mount it anywhere between the boiler and the ?T? where flow gets divided between the HW tank and the CH system?

Does it really matter whether it?s in the boiler flow or return? (It?s a pressurised system).

What?s the state of play regarding pump technology these days? I?m sure that new ones are probably smarter than our old fixed speed one. Any recommendations?

FWIW ours is a 5 bedroom house with 15 radiators.

Tim

[Cynic]

How long has the pump been in operation? Is it really something that needs moving?

[Tim+]

Years. It does absolutely *need* moving but being in the loft makes it harder to access for bleeding or anything else. It?s also poorly placed for transmitting noise to the bedroom below.

The airing cupboard has the boiler?s feed and return pipe running vertically up a wall and would be more accessible.

Tim

[jrwalliker]

I recently replaced ours with a Grundfos UPS3 15-50/65. It is a lot quieter than the old one and has some useful features such as constant-pressure modes. There is also a pulse width modulated output indicating pump power and fault status (and remote speed control if you want) so it might be particularly useful for DIY control systems. It can be fitted in either horizontal or vertical pipe runs so long as the shaft is kept horizontal. John

[Tim+]

Thanks. I?ve just been having a little search online and that was one of the candidates I was thinking about. Relocating it isn?t going to be as simple as I thought though as the present pipework from the boiler to the pump is 28mm (22mm on the output). I seem to recall that this was part of the boiler installation requirements.

To move it would mean extending a lot of 28mm pipework.

Tim

[Tricky Dicky]

The pump should located in the flow pipe work between the boiler and any zone valves.

Richard

[Tim+]

I know that in the days of open vented systems the pump position was important to get right to avoid pumping over, but in this age of pressurised systems, does it make any practical difference if it?s in the flow or return anymore?

Just curious. Not planning on changing it to the return.

Tim

[Davidm]

I can't imagine why, if you have 22mm on the output (to the zone valves?) you can't have 22mm on the input. The flow rate is going to be the same on both side of the pump surely.

[jrwalliker]

If it is mounted in a vertical pipe run, the UPS3 expects to be pumping upwards which might be an issue when the boiler is in the loft. I think this relates to clearing air bubbles efficiently.

John

[Tim+]

Interesting. A case for maybe fitting it to the return then? ;-)

As it happens, I?ve decided against relocating it at the moment. Just going for a straight swap. A job for the future maybe.

Tim

[Tim+]

You?d think so but I do recall that the boiler?s fitting instructions were quite clear about the output pipework having to be 28mm to the pump.

Tim

[newshound]

I thought the more normal recommendation was to put it into the return. Meaning the boiler sees (slightly) higher pressure and is therefore less likely to see boiling in the heat exchanger.

[Roger Hayter]

I had a combi boiler (Firebird) which had two standard Grundfos pumps contrained to pump downwards. They didn't actually last that long - i can't say if that is a coincidence.

[Roger Hayter]

Would that be to reduce turbulence and cavitation in the pump and boiler? Any possible ill effects on the boiler are less likely if the pump is well away from it and the pipe sections near the boiler are still 28mm. And pumps are relatively easy to replace, even if their life is slightly shortened. I would happily ignore that advice if the pump is a long way from the boiler.

[alan_m]

The modern differential pressure proportional speed (power saving) pumps usually have the options for 3 fixed speeds so can be installed on a older system without changing anything. My pump has six proportional speeds plus three fixed speeds.

[alan_m]

One gotcha I had was that the service valves either side of pump leaked when turned back on again after the pump was replaced. I had to partially drain down the system and also replace the 20 year old valves. While the fixing centres from various makes of pump may be standardised the length of (maybe older) service valves is not. The values I purchased were shorter than what I was replacing. In my case it was relatively easy to replace/extend the pipework from my small stock of copper pipe and fittings.

[Clive Arthur]

Just a cautionary tale...

I changed the pump in our pressurised system, this one is inside the boiler. The new one was a three-speed pump. Being a 32kW boiler in a larger house, I turned it all the way up to eleven. Well, three really.

Sometimes there was a rattling noise from the boiler and nearby pipework. Eventually, I realised that this only ever happened when the hot water was heating but not the radiators, and then not every time. This is a much much shorter loop, our cylinder is next to the boiler.

Setting the pump speed to two cured this. Maybe it was cavitation.

[harry]

If it's in the loft it might also be cavitating which also produces a noise.

[Tim+]

I?m sure that?s part of the problem which is one reason I?d like to get it a bit lower.

Tim

[Fredxx]

If its a pressurised system and you're measuring pressure boiler pressure in the loft close to the pump, then I don't believe there is any cavitation.

If there is any doubt, raise the pressure 0.5bar and see if it's quieter.