Wireless sensor networks (WSNs) are being increasingly used in applications where low energy consumption and low cost are the overriding considerations. With increased use, their reliability, availability and serviceability need to be addressed from the outset. Conventional schemes of adding redundant nodes and incorporating reliability in control protocols can effectively improve only the reliability of the overall WSN. The availability and serviceability of WSN nodes can be addressed by providing the remote testing and repair infrastructure for the individual sensor nodes that is well matched with existing on-board test infrastructure, including standard JTAG chains. In this paper, we propose and evaluate scalable architectures of WSN nodes for increased availability as well as implement the proposed solutions using COTS components.