Hi guys long time lurker finally signed up as im in need of help - come to a tennants property today and all the cold taps are hammering when open, and its building up preasure on the hot taps, as soon as a hot is opened the hammering stops.. Im presuming theres a boiler issue here or a crossed pipe at so point. Any help would be great - boiler is a valliant ecotec plus 824
Try turning down the mains stopcock a few turns. Have you had any work done recently involving it being turned off? Have the water board recently fitted a water mater? Have you always had a hammer issue or is it recent? What type of tapas are they? Ceramic disk or washer? Almost certainly not a boiler issue, as when a second tap is opened the issue goes away because you have relieved pressure from one tap to two, I suspect the same would happen if you opened two cold taps.
Thanks for the reply there mate - the thing is it happens with any of the taps, if i run the cold on the whb in the bathroom the hot is the kitchen starts kettling up and the heat/pressure actually forces throufh the shut tap. I was thinking a mixer valve in the boiler could be passing the cold into the dhw and backfilling the pipework?
Also i tried knocking back the stop tap to no avail. The hammering only happens for the first 5 mins of running the water then it stop once the 'pressure' is let off. Really got me stumped so you think its definetly not a boiler fault here?
Could be a mixer tap failed and back feeding or possibly if you have a thermostatic mixer shower that could be the cause. If your taps have ballofix valves on shut each set individually and give it a go, likewise with the shower.